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KVM: x86/mmu: Remove spurious TLB flushes in TDP MMU zap collapsible path

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Drop the "flush" param and return values to/from the TDP MMU's helper for
zapping collapsible SPTEs.  Because the helper runs with mmu_lock held
for read, not write, it uses tdp_mmu_zap_spte_atomic(), and the atomic
zap handles the necessary remote TLB flush.

Similarly, because mmu_lock is dropped and re-acquired between zapping
legacy MMUs and zapping TDP MMUs, kvm_mmu_zap_collapsible_sptes() must
handle remote TLB flushes from the legacy MMU before calling into the TDP
MMU.

Fixes: e2209710cc ("KVM: x86/mmu: Skip rmap operations if rmaps not allocated")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211120045046.3940942-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-11-20 04:50:21 +00:00 committed by Paolo Bonzini
parent 7533377215
commit 4b85c921cd
3 changed files with 11 additions and 25 deletions
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9
arch/x86/kvm/mmu/mmu.c
View File

@ -5848,8 +5848,6 @@ restart:
void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
const struct kvm_memory_slot *slot)
{
bool flush;
if (kvm_memslots_have_rmaps(kvm)) {
write_lock(&kvm->mmu_lock);
/*
@ -5857,17 +5855,14 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
* logging at a 4k granularity and never creates collapsible
* 2m SPTEs during dirty logging.
*/
flush = slot_handle_level_4k(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
if (flush)
if (slot_handle_level_4k(kvm, slot, kvm_mmu_zap_collapsible_spte, true))
kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
write_unlock(&kvm->mmu_lock);
}
if (is_tdp_mmu_enabled(kvm)) {
read_lock(&kvm->mmu_lock);
flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, false);
if (flush)
kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot);
read_unlock(&kvm->mmu_lock);
}
}

22
arch/x86/kvm/mmu/tdp_mmu.c
View File

@ -1362,10 +1362,9 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
* Clear leaf entries which could be replaced by large mappings, for
* GFNs within the slot.
*/
static bool zap_collapsible_spte_range(struct kvm *kvm,
static void zap_collapsible_spte_range(struct kvm *kvm,
struct kvm_mmu_page *root,
const struct kvm_memory_slot *slot,
bool flush)
const struct kvm_memory_slot *slot)
{
gfn_t start = slot->base_gfn;
gfn_t end = start + slot->npages;
@ -1376,10 +1375,8 @@ static bool zap_collapsible_spte_range(struct kvm *kvm,
tdp_root_for_each_pte(iter, root, start, end) {
retry:
if (tdp_mmu_iter_cond_resched(kvm, &iter, flush, true)) {
flush = false;
if (tdp_mmu_iter_cond_resched(kvm, &iter, false, true))
continue;
}
if (!is_shadow_present_pte(iter.old_spte) ||
!is_last_spte(iter.old_spte, iter.level))
@ -1391,6 +1388,7 @@ retry:
pfn, PG_LEVEL_NUM))
continue;
/* Note, a successful atomic zap also does a remote TLB flush. */
if (!tdp_mmu_zap_spte_atomic(kvm, &iter)) {
/*
* The iter must explicitly re-read the SPTE because
@ -1399,30 +1397,24 @@ retry:
iter.old_spte = READ_ONCE(*rcu_dereference(iter.sptep));
goto retry;
}
flush = true;
}
rcu_read_unlock();
return flush;
}
/*
* Clear non-leaf entries (and free associated page tables) which could
* be replaced by large mappings, for GFNs within the slot.
*/
bool kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
const struct kvm_memory_slot *slot,
bool flush)
void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
const struct kvm_memory_slot *slot)
{
struct kvm_mmu_page *root;
lockdep_assert_held_read(&kvm->mmu_lock);
for_each_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, true)
flush = zap_collapsible_spte_range(kvm, root, slot, flush);
return flush;
zap_collapsible_spte_range(kvm, root, slot);
}
/*

5
arch/x86/kvm/mmu/tdp_mmu.h
View File

@ -64,9 +64,8 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
struct kvm_memory_slot *slot,
gfn_t gfn, unsigned long mask,
bool wrprot);
bool kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
const struct kvm_memory_slot *slot,
bool flush);
void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
const struct kvm_memory_slot *slot);
bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm,
struct kvm_memory_slot *slot, gfn_t gfn,