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KVM: x86/mmu: Fully re-evaluate MMIO caching when SPTE masks change

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Fully re-evaluate whether or not MMIO caching can be enabled when SPTE
masks change; simply clearing enable_mmio_caching when a configuration
isn't compatible with caching fails to handle the scenario where the
masks are updated, e.g. by VMX for EPT or by SVM to account for the C-bit
location, and toggle compatibility from false=>true.

Snapshot the original module param so that re-evaluating MMIO caching
preserves userspace's desire to allow caching.  Use a snapshot approach
so that enable_mmio_caching still reflects KVM's actual behavior.

Fixes: 8b9e74bfbf8c ("KVM: x86/mmu: Use enable_mmio_caching to track if MMIO caching is enabled")
Reported-by: Michael Roth <michael.roth@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Tested-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-Id: <20220803224957.1285926-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-08-03 22:49:56 +00:00 committed by Paolo Bonzini
parent 982bae43f1
commit c3e0c8c2e8
3 changed files with 24 additions and 0 deletions
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4
arch/x86/kvm/mmu/mmu.c
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@ -6697,11 +6697,15 @@ static int set_nx_huge_pages(const char *val, const struct kernel_param *kp)
/*
* nx_huge_pages needs to be resolved to true/false when kvm.ko is loaded, as
* its default value of -1 is technically undefined behavior for a boolean.
* Forward the module init call to SPTE code so that it too can handle module
* params that need to be resolved/snapshot.
*/
void __init kvm_mmu_x86_module_init(void)
{
if (nx_huge_pages == -1)
__set_nx_huge_pages(get_nx_auto_mode());
kvm_mmu_spte_module_init();
}
/*

19
arch/x86/kvm/mmu/spte.c
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@ -20,6 +20,7 @@
#include <asm/vmx.h>
bool __read_mostly enable_mmio_caching = true;
static bool __ro_after_init allow_mmio_caching;
module_param_named(mmio_caching, enable_mmio_caching, bool, 0444);
u64 __read_mostly shadow_host_writable_mask;
@ -43,6 +44,18 @@ u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
u8 __read_mostly shadow_phys_bits;
void __init kvm_mmu_spte_module_init(void)
{
/*
* Snapshot userspace's desire to allow MMIO caching. Whether or not
* KVM can actually enable MMIO caching depends on vendor-specific
* hardware capabilities and other module params that can't be resolved
* until the vendor module is loaded, i.e. enable_mmio_caching can and
* will change when the vendor module is (re)loaded.
*/
allow_mmio_caching = enable_mmio_caching;
}
static u64 generation_mmio_spte_mask(u64 gen)
{
u64 mask;
@ -340,6 +353,12 @@ void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask)
BUG_ON((u64)(unsigned)access_mask != access_mask);
WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask);
/*
* Reset to the original module param value to honor userspace's desire
* to (dis)allow MMIO caching. Update the param itself so that
* userspace can see whether or not KVM is actually using MMIO caching.
*/
enable_mmio_caching = allow_mmio_caching;
if (!enable_mmio_caching)
mmio_value = 0;

1
arch/x86/kvm/mmu/spte.h
View File

@ -450,6 +450,7 @@ static inline u64 restore_acc_track_spte(u64 spte)
u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn);
void __init kvm_mmu_spte_module_init(void);
void kvm_mmu_reset_all_pte_masks(void);
#endif