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KVM: Don't take mmu_lock for range invalidation unless necessary

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Avoid taking mmu_lock for .invalidate_range_{start,end}() notifications
that are unrelated to KVM.  This is possible now that memslot updates are
blocked from range_start() to range_end(); that ensures that lock elision
happens in both or none, and therefore that mmu_notifier_count updates
(which must occur while holding mmu_lock for write) are always paired
across start->end.

Based on patches originally written by Ben Gardon.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2021-08-03 03:45:41 -04:00
parent 52ac8b358b
commit 071064f14d
1 changed files with 12 additions and 13 deletions
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25
virt/kvm/kvm_main.c
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@ -496,17 +496,6 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
idx = srcu_read_lock(&kvm->srcu);
/* The on_lock() path does not yet support lock elision. */
if (!IS_KVM_NULL_FN(range->on_lock)) {
locked = true;
KVM_MMU_LOCK(kvm);
range->on_lock(kvm, range->start, range->end);
if (IS_KVM_NULL_FN(range->handler))
goto out_unlock;
}
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
slots = __kvm_memslots(kvm, i);
kvm_for_each_memslot(slot, slots) {
@ -538,6 +527,10 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
if (!locked) {
locked = true;
KVM_MMU_LOCK(kvm);
if (!IS_KVM_NULL_FN(range->on_lock))
range->on_lock(kvm, range->start, range->end);
if (IS_KVM_NULL_FN(range->handler))
break;
}
ret |= range->handler(kvm, &gfn_range);
}
@ -546,7 +539,6 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
if (range->flush_on_ret && (ret || kvm->tlbs_dirty))
kvm_flush_remote_tlbs(kvm);
out_unlock:
if (locked)
KVM_MMU_UNLOCK(kvm);
@ -605,8 +597,14 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
/*
* .change_pte() must be surrounded by .invalidate_range_{start,end}().
* If mmu_notifier_count is zero, then no in-progress invalidations,
* including this one, found a relevant memslot at start(); rechecking
* memslots here is unnecessary. Note, a false positive (count elevated
* by a different invalidation) is sub-optimal but functionally ok.
*/
WARN_ON_ONCE(!READ_ONCE(kvm->mn_active_invalidate_count));
if (!READ_ONCE(kvm->mmu_notifier_count))
return;
kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
}
@ -1398,7 +1396,8 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
/*
* Do not store the new memslots while there are invalidations in
* progress (preparatory change for the next commit).
* progress, otherwise the locking in invalidate_range_start and
* invalidate_range_end will be unbalanced.
*/
spin_lock(&kvm->mn_invalidate_lock);
prepare_to_rcuwait(&kvm->mn_memslots_update_rcuwait);