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- Add back a comment about the subtle side effect of try_cmpxchg64() in
tdp_mmu_set_spte_atomic()
- Add an assertion in __kvm_mmu_invalidate_addr() to verify that the target
KVM MMU is the current MMU
- Add a "never" option to effectively avoid creating NX hugepage recovery
threads
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Merge tag 'kvm-x86-mmu-6.5' of https://github.com/kvm-x86/linux into HEAD
KVM x86/mmu changes for 6.5:
- Add back a comment about the subtle side effect of try_cmpxchg64() in
tdp_mmu_set_spte_atomic()
- Add an assertion in __kvm_mmu_invalidate_addr() to verify that the target
KVM MMU is the current MMU
- Add a "never" option to effectively avoid creating NX hugepage recovery
threads
Add a "never" option to the nx_huge_pages module param to allow userspace
to do a one-way hard disabling of the mitigation, and don't create the
per-VM recovery threads when the mitigation is hard disabled. Letting
userspace pinky swear that userspace doesn't want to enable NX mitigation
(without reloading KVM) allows certain use cases to avoid the latency
problems associated with spawning a kthread for each VM.
E.g. in FaaS use cases, the guest kernel is trusted and the host may
create 100+ VMs per logical CPU, which can result in 100ms+ latencies when
a burst of VMs is created.
Reported-by: Li RongQing <lirongqing@baidu.com>
Closes: https://lore.kernel.org/all/1679555884-32544-1-git-send-email-lirongqing@baidu.com
Cc: Yong He <zhuangel570@gmail.com>
Cc: Robert Hoo <robert.hoo.linux@gmail.com>
Cc: Kai Huang <kai.huang@intel.com>
Reviewed-by: Robert Hoo <robert.hoo.linux@gmail.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Tested-by: Luiz Capitulino <luizcap@amazon.com>
Reviewed-by: Li RongQing <lirongqing@baidu.com>
Link: https://lore.kernel.org/r/20230602005859.784190-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Request an APIC-access page reload when the backing page is migrated (or
unmapped) if and only if vendor code actually plugs the backing pfn into
structures that reside outside of KVM's MMU. This avoids kicking all
vCPUs in the (hopefully infrequent) scenario where the backing page is
migrated/invalidated.
Unlike VMX's APICv, SVM's AVIC doesn't plug the backing pfn directly into
the VMCB and so doesn't need a hook to invalidate an out-of-MMU "mapping".
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20230602011518.787006-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Now that KVM honors past and in-progress mmu_notifier invalidations when
reloading the APIC-access page, use KVM's "standard" invalidation hooks
to trigger a reload and delete the one-off usage of invalidate_range().
Aside from eliminating one-off code in KVM, dropping KVM's use of
invalidate_range() will allow common mmu_notifier to redefine the API to
be more strictly focused on invalidating secondary TLBs that share the
primary MMU's page tables.
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20230602011518.787006-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Factor in the address space (non-SMM vs. SMM) of the target shadow page
when recovering potential NX huge pages, otherwise KVM will retrieve the
wrong memslot when zapping shadow pages that were created for SMM. The
bug most visibly manifests as a WARN on the memslot being non-NULL, but
the worst case scenario is that KVM could unaccount the shadow page
without ensuring KVM won't install a huge page, i.e. if the non-SMM slot
is being dirty logged, but the SMM slot is not.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 3911 at arch/x86/kvm/mmu/mmu.c:7015
kvm_nx_huge_page_recovery_worker+0x38c/0x3d0 [kvm]
CPU: 1 PID: 3911 Comm: kvm-nx-lpage-re
RIP: 0010:kvm_nx_huge_page_recovery_worker+0x38c/0x3d0 [kvm]
RSP: 0018:ffff99b284f0be68 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff99b284edd000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff9271397024e0 R08: 0000000000000000 R09: ffff927139702450
R10: 0000000000000000 R11: 0000000000000001 R12: ffff99b284f0be98
R13: 0000000000000000 R14: ffff9270991fcd80 R15: 0000000000000003
FS: 0000000000000000(0000) GS:ffff927f9f640000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0aacad3ae0 CR3: 000000088fc2c005 CR4: 00000000003726e0
Call Trace:
<TASK>
__pfx_kvm_nx_huge_page_recovery_worker+0x10/0x10 [kvm]
kvm_vm_worker_thread+0x106/0x1c0 [kvm]
kthread+0xd9/0x100
ret_from_fork+0x2c/0x50
</TASK>
---[ end trace 0000000000000000 ]---
This bug was exposed by commit edbdb43fc96b ("KVM: x86: Preserve TDP MMU
roots until they are explicitly invalidated"), which allowed KVM to retain
SMM TDP MMU roots effectively indefinitely. Before commit edbdb43fc96b,
KVM would zap all SMM TDP MMU roots and thus all SMM TDP MMU shadow pages
once all vCPUs exited SMM, which made the window where this bug (recovering
an SMM NX huge page) could be encountered quite tiny. To hit the bug, the
NX recovery thread would have to run while at least one vCPU was in SMM.
Most VMs typically only use SMM during boot, and so the problematic shadow
pages were gone by the time the NX recovery thread ran.
Now that KVM preserves TDP MMU roots until they are explicitly invalidated
(e.g. by a memslot deletion), the window to trigger the bug is effectively
never closed because most VMMs don't delete memslots after boot (except
for a handful of special scenarios).
Fixes: eb298605705a ("KVM: x86/mmu: Do not recover dirty-tracked NX Huge Pages")
Reported-by: Fabio Coatti <fabio.coatti@gmail.com>
Closes: https://lore.kernel.org/all/CADpTngX9LESCdHVu_2mQkNGena_Ng2CphWNwsRGSMxzDsTjU2A@mail.gmail.com
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230602010137.784664-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Add assertion to track that "mmu == vcpu->arch.mmu" is always true in the
context of __kvm_mmu_invalidate_addr(). for_each_shadow_entry_using_root()
and kvm_sync_spte() operate on vcpu->arch.mmu, but the only reason that
doesn't cause explosions is because handle_invept() frees roots instead of
doing a manual invalidation. As of now, there are no major roadblocks
to switching INVEPT emulation over to use kvm_mmu_invalidate_addr().
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Like Xu <likexu@tencent.com>
Link: https://lore.kernel.org/r/20230523032947.60041-1-likexu@tencent.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Commit aee98a6838d5 ("KVM: x86/mmu: Use try_cmpxchg64 in
tdp_mmu_set_spte_atomic") removed the comment that iter->old_spte is
updated when different logical CPU modifies the page table entry.
Although this is what try_cmpxchg does implicitly, it won't hurt
if this fact is explicitly mentioned in a restored comment.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: David Matlack <dmatlack@google.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20230425113932.3148-1-ubizjak@gmail.com
[sean: extend comment above try_cmpxchg64()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
result in the root being freed even though the root is completely valid and
can be reused as-is (with a TLB flush).
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Merge tag 'kvm-x86-mmu-6.4-2' of https://github.com/kvm-x86/linux into HEAD
Fix a long-standing flaw in x86's TDP MMU where unloading roots on a vCPU can
result in the root being freed even though the root is completely valid and
can be reused as-is (with a TLB flush).
Preserve TDP MMU roots until they are explicitly invalidated by gifting
the TDP MMU itself a reference to a root when it is allocated. Keeping a
reference in the TDP MMU fixes a flaw where the TDP MMU exhibits terrible
performance, and can potentially even soft-hang a vCPU, if a vCPU
frequently unloads its roots, e.g. when KVM is emulating SMI+RSM.
When KVM emulates something that invalidates _all_ TLB entries, e.g. SMI
and RSM, KVM unloads all of the vCPUs roots (KVM keeps a small per-vCPU
cache of previous roots). Unloading roots is a simple way to ensure KVM
flushes and synchronizes all roots for the vCPU, as KVM flushes and syncs
when allocating a "new" root (from the vCPU's perspective).
In the shadow MMU, KVM keeps track of all shadow pages, roots included, in
a per-VM hash table. Unloading a shadow MMU root just wipes it from the
per-vCPU cache; the root is still tracked in the per-VM hash table. When
KVM loads a "new" root for the vCPU, KVM will find the old, unloaded root
in the per-VM hash table.
Unlike the shadow MMU, the TDP MMU doesn't track "inactive" roots in a
per-VM structure, where "active" in this case means a root is either
in-use or cached as a previous root by at least one vCPU. When a TDP MMU
root becomes inactive, i.e. the last vCPU reference to the root is put,
KVM immediately frees the root (asterisk on "immediately" as the actual
freeing may be done by a worker, but for all intents and purposes the root
is gone).
The TDP MMU behavior is especially problematic for 1-vCPU setups, as
unloading all roots effectively frees all roots. The issue is mitigated
to some degree in multi-vCPU setups as a different vCPU usually holds a
reference to an unloaded root and thus keeps the root alive, allowing the
vCPU to reuse its old root after unloading (with a flush+sync).
The TDP MMU flaw has been known for some time, as until very recently,
KVM's handling of CR0.WP also triggered unloading of all roots. The
CR0.WP toggling scenario was eventually addressed by not unloading roots
when _only_ CR0.WP is toggled, but such an approach doesn't Just Work
for emulating SMM as KVM must emulate a full TLB flush on entry and exit
to/from SMM. Given that the shadow MMU plays nice with unloading roots
at will, teaching the TDP MMU to do the same is far less complex than
modifying KVM to track which roots need to be flushed before reuse.
Note, preserving all possible TDP MMU roots is not a concern with respect
to memory consumption. Now that the role for direct MMUs doesn't include
information about the guest, e.g. CR0.PG, CR0.WP, CR4.SMEP, etc., there
are _at most_ six possible roots (where "guest_mode" here means L2):
1. 4-level !SMM !guest_mode
2. 4-level SMM !guest_mode
3. 5-level !SMM !guest_mode
4. 5-level SMM !guest_mode
5. 4-level !SMM guest_mode
6. 5-level !SMM guest_mode
And because each vCPU can track 4 valid roots, a VM can already have all
6 root combinations live at any given time. Not to mention that, in
practice, no sane VMM will advertise different guest.MAXPHYADDR values
across vCPUs, i.e. KVM won't ever use both 4-level and 5-level roots for
a single VM. Furthermore, the vast majority of modern hypervisors will
utilize EPT/NPT when available, thus the guest_mode=%true cases are also
unlikely to be utilized.
Reported-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Link: https://lore.kernel.org/all/959c5bce-beb5-b463-7158-33fc4a4f910c@linux.microsoft.com
Link: https://lkml.kernel.org/r/20220209170020.1775368-1-pbonzini%40redhat.com
Link: https://lore.kernel.org/all/20230322013731.102955-1-minipli@grsecurity.net
Link: https://lore.kernel.org/all/000000000000a0bc2b05f9dd7fab@google.com
Link: https://lore.kernel.org/all/000000000000eca0b905fa0f7756@google.com
Cc: Ben Gardon <bgardon@google.com>
Cc: David Matlack <dmatlack@google.com>
Cc: stable@vger.kernel.org
Tested-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Link: https://lore.kernel.org/r/20230426220323.3079789-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
- Disallow virtualizing legacy LBRs if architectural LBRs are available,
the two are mutually exclusive in hardware
- Disallow writes to immutable feature MSRs (notably PERF_CAPABILITIES)
after KVM_RUN, and overhaul the vmx_pmu_caps selftest to better
validate PERF_CAPABILITIES
- Apply PMU filters to emulated events and add test coverage to the
pmu_event_filter selftest
- Misc cleanups and fixes
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Merge tag 'kvm-x86-pmu-6.4' of https://github.com/kvm-x86/linux into HEAD
KVM x86 PMU changes for 6.4:
- Disallow virtualizing legacy LBRs if architectural LBRs are available,
the two are mutually exclusive in hardware
- Disallow writes to immutable feature MSRs (notably PERF_CAPABILITIES)
after KVM_RUN, and overhaul the vmx_pmu_caps selftest to better
validate PERF_CAPABILITIES
- Apply PMU filters to emulated events and add test coverage to the
pmu_event_filter selftest
- Misc cleanups and fixes
- Tweak FNAME(sync_spte) to avoid unnecessary writes+flushes when the
guest is only adding new PTEs
- Overhaul .sync_page() and .invlpg() to share the .sync_page()
implementation, i.e. utilize .sync_page()'s optimizations when emulating
invalidations
- Clean up the range-based flushing APIs
- Revamp the TDP MMU's reaping of Accessed/Dirty bits to clear a single
A/D bit using a LOCK AND instead of XCHG, and skip all of the "handle
changed SPTE" overhead associated with writing the entire entry
- Track the number of "tail" entries in a pte_list_desc to avoid having
to walk (potentially) all descriptors during insertion and deletion,
which gets quite expensive if the guest is spamming fork()
- Misc cleanups
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Merge tag 'kvm-x86-mmu-6.4' of https://github.com/kvm-x86/linux into HEAD
KVM x86 MMU changes for 6.4:
- Tweak FNAME(sync_spte) to avoid unnecessary writes+flushes when the
guest is only adding new PTEs
- Overhaul .sync_page() and .invlpg() to share the .sync_page()
implementation, i.e. utilize .sync_page()'s optimizations when emulating
invalidations
- Clean up the range-based flushing APIs
- Revamp the TDP MMU's reaping of Accessed/Dirty bits to clear a single
A/D bit using a LOCK AND instead of XCHG, and skip all of the "handle
changed SPTE" overhead associated with writing the entire entry
- Track the number of "tail" entries in a pte_list_desc to avoid having
to walk (potentially) all descriptors during insertion and deletion,
which gets quite expensive if the guest is spamming fork()
- Misc cleanups
Refresh the MMU's snapshot of the vCPU's CR0.WP prior to checking for
permission faults when emulating a guest memory access and CR0.WP may be
guest owned. If the guest toggles only CR0.WP and triggers emulation of
a supervisor write, e.g. when KVM is emulating UMIP, KVM may consume a
stale CR0.WP, i.e. use stale protection bits metadata.
Note, KVM passes through CR0.WP if and only if EPT is enabled as CR0.WP
is part of the MMU role for legacy shadow paging, and SVM (NPT) doesn't
support per-bit interception controls for CR0. Don't bother checking for
EPT vs. NPT as the "old == new" check will always be true under NPT, i.e.
the only cost is the read of vcpu->arch.cr4 (SVM unconditionally grabs CR0
from the VMCB on VM-Exit).
Reported-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lkml.kernel.org/r/677169b4-051f-fcae-756b-9a3e1bb9f8fe%40grsecurity.net
Fixes: fb509f76acc8 ("KVM: VMX: Make CR0.WP a guest owned bit")
Tested-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20230405002608.418442-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Refactor Hyper-V's range-based TLB flushing API to take a gfn+nr_pages
pair instead of a struct, and bury said struct in Hyper-V specific code.
Passing along two params generates much better code for the common case
where KVM is _not_ running on Hyper-V, as forwarding the flush on to
Hyper-V's hv_flush_remote_tlbs_range() from kvm_flush_remote_tlbs_range()
becomes a tail call.
Cc: David Matlack <dmatlack@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20230405003133.419177-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Rename the Hyper-V hooks for TLB flushing to match the naming scheme used
by all the other TLB flushing hooks, e.g. in kvm_x86_ops, vendor code,
arch hooks from common code, etc.
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20230405003133.419177-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Add a helper to query if a vCPU has run so that KVM doesn't have to open
code the check on last_vmentry_cpu being set to a magic value.
No functional change intended.
Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Like Xu <like.xu.linux@gmail.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20230311004618.920745-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Merge __handle_changed_pte() and handle_changed_spte_acc_track() into a
single function, handle_changed_pte(), as the two are always used
together. Remove the existing handle_changed_pte(), as it's just a
wrapper that calls __handle_changed_pte() and
handle_changed_spte_acc_track().
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[sean: massage changelog]
Link: https://lore.kernel.org/r/20230321220021.2119033-14-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Remove handle_changed_spte_dirty_log() as there is no code flow which
sets 4KiB SPTE writable and hit this path. This function marks the page
dirty in a memslot only if new SPTE is 4KiB in size and writable.
Current users of handle_changed_spte_dirty_log() are:
1. set_spte_gfn() - Create only non writable SPTEs.
2. write_protect_gfn() - Change an SPTE to non writable.
3. zap leaf and roots APIs - Everything is 0.
4. handle_removed_pt() - Sets SPTEs to REMOVED_SPTE
5. tdp_mmu_link_sp() - Makes non leaf SPTEs.
There is also no path which creates a writable 4KiB without going
through make_spte() and this functions takes care of marking SPTE dirty
in the memslot if it is PT_WRITABLE.
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[sean: add blurb to __handle_changed_spte()'s comment]
Link: https://lore.kernel.org/r/20230321220021.2119033-13-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Remove bool parameter "record_acc_track" from __tdp_mmu_set_spte() and
refactor the code. This variable is always set to true by its caller.
Remove single and double underscore prefix from tdp_mmu_set_spte()
related APIs:
1. Change __tdp_mmu_set_spte() to tdp_mmu_set_spte()
2. Change _tdp_mmu_set_spte() to tdp_mmu_iter_set_spte()
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20230321220021.2119033-12-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Drop everything except the "tdp_mmu_spte_changed" tracepoint part of
__handle_changed_spte() when aging SPTEs in the TDP MMU, as clearing the
accessed status doesn't affect the SPTE's shadow-present status, whether
or not the SPTE is a leaf, or change the PFN. I.e. none of the functional
updates handled by __handle_changed_spte() are relevant.
Losing __handle_changed_spte()'s sanity checks does mean that a bug could
theoretical go unnoticed, but that scenario is extremely unlikely, e.g.
would effectively require a misconfigured MMU or a locking bug elsewhere.
Link: https://lore.kernel.org/all/Y9HcHRBShQgjxsQb@google.com
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[sean: massage changelog]
Link: https://lore.kernel.org/r/20230321220021.2119033-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Drop the unnecessary call to handle dirty log updates when aging TDP MMU
SPTEs, as neither clearing the Accessed bit nor marking a SPTE for access
tracking can _set_ the Writable bit, i.e. can't trigger marking a gfn
dirty in its memslot. The access tracking path can _clear_ the Writable
bit, e.g. if the XCHG races with fast_page_fault() and writes the stale
value without the Writable bit set, but clearing the Writable bit outside
of mmu_lock is not allowed, i.e. access tracking can't spuriously set the
Writable bit.
Signed-off-by: Vipin Sharma <vipinsh@google.com>
[sean: split to separate patch, apply to dirty path, write changelog]
Link: https://lore.kernel.org/r/20230321220021.2119033-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Use tdp_mmu_clear_spte_bits() when clearing the Accessed bit in TDP MMU
SPTEs so as to use an atomic-AND instead of XCHG to clear the A-bit.
Similar to the D-bit story, this will allow KVM to bypass
__handle_changed_spte() by ensuring only the A-bit is modified.
Link: https://lore.kernel.org/all/Y9HcHRBShQgjxsQb@google.com
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[sean: massage changelog]
Link: https://lore.kernel.org/r/20230321220021.2119033-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Remove bool parameter "record_dirty_log" from __tdp_mmu_set_spte() and
refactor the code as this variable is always set to true by its caller.
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20230321220021.2119033-8-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Drop everything except marking the PFN dirty and the relevant tracepoint
parts of __handle_changed_spte() when clearing the dirty status of gfns in
the TDP MMU. Clearing only the Dirty (or Writable) bit doesn't affect
the SPTEs shadow-present status, whether or not the SPTE is a leaf, or
change the SPTE's PFN. I.e. other than marking the PFN dirty, none of the
functional updates handled by __handle_changed_spte() are relevant.
Losing __handle_changed_spte()'s sanity checks does mean that a bug could
theoretical go unnoticed, but that scenario is extremely unlikely, e.g.
would effectively require a misconfigured or a locking bug elsewhere.
Opportunistically remove a comment blurb from __handle_changed_spte()
about all modifications to TDP MMU SPTEs needing to invoke said function,
that "rule" hasn't been true since fast page fault support was added for
the TDP MMU (and perhaps even before).
Tested on a VM (160 vCPUs, 160 GB memory) and found that performance of
clear dirty log stage improved by ~40% in dirty_log_perf_test (with the
full optimization applied).
Before optimization:
--------------------
Iteration 1 clear dirty log time: 3.638543593s
Iteration 2 clear dirty log time: 3.145032742s
Iteration 3 clear dirty log time: 3.142340358s
Clear dirty log over 3 iterations took 9.925916693s. (Avg 3.308638897s/iteration)
After optimization:
-------------------
Iteration 1 clear dirty log time: 2.318988110s
Iteration 2 clear dirty log time: 1.794470164s
Iteration 3 clear dirty log time: 1.791668628s
Clear dirty log over 3 iterations took 5.905126902s. (Avg 1.968375634s/iteration)
Link: https://lore.kernel.org/all/Y9hXmz%2FnDOr1hQal@google.com
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[sean: split the switch to atomic-AND to a separate patch]
Link: https://lore.kernel.org/r/20230321220021.2119033-7-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Drop the unnecessary call to handle access-tracking changes when clearing
the dirty status of TDP MMU SPTEs. Neither the Dirty bit nor the Writable
bit has any impact on the accessed state of a page, i.e. clearing only
the aforementioned bits doesn't make an accessed SPTE suddently not
accessed.
Signed-off-by: Vipin Sharma <vipinsh@google.com>
[sean: split to separate patch, write changelog]
Link: https://lore.kernel.org/r/20230321220021.2119033-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Optimize the clearing of dirty state in TDP MMU SPTEs by doing an
atomic-AND (on SPTEs that have volatile bits) instead of the full XCHG
that currently ends up being invoked (see kvm_tdp_mmu_write_spte()).
Clearing _only_ the bit in question will allow KVM to skip the many
irrelevant checks in __handle_changed_spte() by avoiding any collateral
damage due to the XCHG writing all SPTE bits, e.g. the XCHG could race
with fast_page_fault() setting the W-bit and the CPU setting the D-bit,
and thus incorrectly drop the CPU's D-bit update.
Link: https://lore.kernel.org/all/Y9hXmz%2FnDOr1hQal@google.com
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[sean: split the switch to atomic-AND to a separate patch]
Link: https://lore.kernel.org/r/20230321220021.2119033-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Deduplicate the guts of the TDP MMU's clearing of dirty status by
snapshotting whether to check+clear the Dirty bit vs. the Writable bit,
which is the only difference between the two flavors of dirty tracking.
Note, kvm_ad_enabled() is just a wrapper for shadow_accessed_mask, i.e.
is constant after kvm-{intel,amd}.ko is loaded.
Link: https://lore.kernel.org/all/Yz4Qi7cn7TWTWQjj@google.com
Signed-off-by: Vipin Sharma <vipinsh@google.com>
[sean: split to separate patch, apply to dirty log, write changelog]
Link: https://lore.kernel.org/r/20230321220021.2119033-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Use the constant-after-module-load kvm_ad_enabled() to check if SPTEs in
the TDP MMU need to be write-protected when clearing accessed/dirty status
instead of manually checking every SPTE. The per-SPTE A/D enabling is
specific to nested EPT MMUs, i.e. when KVM is using EPT A/D bits but L1 is
not, and so cannot happen in the TDP MMU (which is non-nested only).
Keep the original code as sanity checks buried under MMU_WARN_ON().
MMU_WARN_ON() is more or less useless at the moment, but there are plans
to change that.
Link: https://lore.kernel.org/all/Yz4Qi7cn7TWTWQjj@google.com
Signed-off-by: Vipin Sharma <vipinsh@google.com>
[sean: split to separate patch, apply to dirty path, write changelog]
Link: https://lore.kernel.org/r/20230321220021.2119033-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Move conditions in kvm_tdp_mmu_write_spte() to check if an SPTE should
be written atomically or not to a separate function.
This new function, kvm_tdp_mmu_spte_need_atomic_write(), will be used
in future commits to optimize clearing bits in SPTEs.
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Link: https://lore.kernel.org/r/20230321220021.2119033-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Most of the time, calls to get_guest_pgd result in calling
kvm_read_cr3 (the exception is only nested TDP). Hardcode
the default instead of using the get_cr3 function, avoiding
a retpoline if they are enabled.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20230322013731.102955-2-minipli@grsecurity.net
Signed-off-by: Sean Christopherson <seanjc@google.com>
Adjust a variety of functions in mmu.c to put the function return type on
the same line as the function declaration. As stated in the Linus
specification:
But the "on their own line" is complete garbage to begin with. That
will NEVER be a kernel rule. We should never have a rule that assumes
things are so long that they need to be on multiple lines.
We don't put function return types on their own lines either, even if
some other projects have that rule (just to get function names at the
beginning of lines or some other odd reason).
Leave the functions generated by BUILD_MMU_ROLE_REGS_ACCESSOR() as-is,
that code is basically illegible no matter how it's formatted.
No functional change intended.
Link: https://lore.kernel.org/mm-commits/CAHk-=wjS-Jg7sGMwUPpDsjv392nDOOs0CtUtVkp=S6Q7JzFJRw@mail.gmail.com
Signed-off-by: Ben Gardon <bgardon@google.com>
Link: https://lore.kernel.org/r/20230202182809.1929122-4-bgardon@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Assert that mmu_lock is held for write in __walk_slot_rmaps() instead of
hoping the function comment will magically prevent introducing bugs.
Signed-off-by: Ben Gardon <bgardon@google.com>
Link: https://lore.kernel.org/r/20230202182809.1929122-3-bgardon@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Use gfn_t instead of u64 for kvm_flush_remote_tlbs_range()'s parameters,
since gfn_t is the standard type for GFNs throughout KVM.
Opportunistically rename pages to nr_pages to make its role even more
obvious.
No functional change intended.
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20230126184025.2294823-6-dmatlack@google.com
[sean: convert pages to gfn_t too, and rename]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Rename kvm_flush_remote_tlbs_with_address() to
kvm_flush_remote_tlbs_range(). This name is shorter, which reduces the
number of callsites that need to be broken up across multiple lines, and
more readable since it conveys a range of memory is being flushed rather
than a single address.
No functional change intended.
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20230126184025.2294823-5-dmatlack@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Collapse kvm_flush_remote_tlbs_with_range() and
kvm_flush_remote_tlbs_with_address() into a single function. This
eliminates some lines of code and a useless NULL check on the range
struct.
Opportunistically switch from ENOTSUPP to EOPNOTSUPP to make checkpatch
happy.
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20230126184025.2294823-4-dmatlack@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Rework "struct pte_list_desc" and pte_list_{add|remove} to track the tail
count, i.e. number of PTEs in non-head descriptors, and to always keep all
tail descriptors full so that adding a new entry and counting the number
of entries is done in constant time instead of linear time.
No visible performace is changed in tests. But pte_list_add() is no longer
shown in the perf result for the COWed pages even the guest forks millions
of tasks.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230113122910.672417-1-jiangshanlai@gmail.com
[sean: reword shortlog, tweak changelog, add lots of comments, add BUG_ON()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Sync the spte only when the spte is set and avoid the indirect branch.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216235321.735214-5-jiangshanlai@gmail.com
[sean: add wrapper instead of open coding each check]
Signed-off-by: Sean Christopherson <seanjc@google.com>
In hardware TLB, invalidating TLB entries means the translations are
removed from the TLB.
In KVM shadowed vTLB, the translations (combinations of shadow paging
and hardware TLB) are generally maintained as long as they remain "clean"
when the TLB of an address space (i.e. a PCID or all) is flushed with
the help of write-protections, sp->unsync, and kvm_sync_page(), where
"clean" in this context means that no updates to KVM's SPTEs are needed.
However, FNAME(invlpg) always zaps/removes the vTLB if the shadow page is
unsync, and thus triggers a remote flush even if the original vTLB entry
is clean, i.e. is usable as-is.
Besides this, FNAME(invlpg) is largely is a duplicate implementation of
FNAME(sync_spte) to invalidate a vTLB entry.
To address both issues, reuse FNAME(sync_spte) to share the code and
slightly modify the semantics, i.e. keep the vTLB entry if it's "clean"
and avoid remote TLB flush.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216235321.735214-3-jiangshanlai@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Don't assume the current root to be valid, just check it and remove
the WARN().
Also move the code to check if the root is valid into FNAME(invlpg)
to simplify the code.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216235321.735214-2-jiangshanlai@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Use kvm_mmu_invalidate_addr() instead open calls to mmu->invlpg().
No functional change intended.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216235321.735214-1-jiangshanlai@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
The @root_hpa for kvm_mmu_invalidate_addr() is called with @mmu->root.hpa
or INVALID_PAGE where @mmu->root.hpa is to invalidate gva for the current
root (the same meaning as KVM_MMU_ROOT_CURRENT) and INVALID_PAGE is to
invalidate gva for all roots (the same meaning as KVM_MMU_ROOTS_ALL).
Change the argument type of kvm_mmu_invalidate_addr() and use
KVM_MMU_ROOT_XXX instead so that we can reuse the function for
kvm_mmu_invpcid_gva() and nested_ept_invalidate_addr() for invalidating
gva for different set of roots.
No fuctionalities changed.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216154115.710033-9-jiangshanlai@gmail.com
[sean: massage comment slightly]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tweak KVM_MMU_ROOTS_ALL to precisely cover all current+previous root
flags, and add a sanity in kvm_mmu_free_roots() to verify that the set
of roots to free doesn't stray outside KVM_MMU_ROOTS_ALL.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216154115.710033-8-jiangshanlai@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Sometimes when the guest updates its pagetable, it adds only new gptes
to it without changing any existed one, so there is no point to update
the sptes for these existed gptes.
Also when the sptes for these unchanged gptes are updated, the AD
bits are also removed since make_spte() is called with prefetch=true
which might result unneeded TLB flushing.
Just do nothing if the gpte's permissions are unchanged.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216154115.710033-7-jiangshanlai@gmail.com
[sean: expand comment to call out A/D bits]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Rename mmu->sync_page to mmu->sync_spte and move the code out
of FNAME(sync_page)'s loop body into mmu.c.
No functionalities change intended.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216154115.710033-6-jiangshanlai@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
mmu->sync_page for direct paging is never called.
And both mmu->sync_page and mm->invlpg only make sense in shadow paging.
Setting mmu->sync_page as NULL for direct paging makes it consistent
with mm->invlpg which is set NULL for the case.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216154115.710033-5-jiangshanlai@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Assert that mmu->sync_page is non-NULL as part of the sanity checks
performed before attempting to sync a shadow page. Explicitly checking
mmu->sync_page is all but guaranteed to be redundant with the existing
sanity check that the MMU is indirect, but the cost is negligible, and
the explicit check also serves as documentation.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216154115.710033-4-jiangshanlai@gmail.com
[sean: increase verbosity of changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
