Commit 4b85c921 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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



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: e2209710 ("KVM: x86/mmu: Skip rmap operations if rmaps not allocated")
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20211120045046.3940942-4-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 75333772

arch/x86/kvm/mmu/mmu.c

+2 −7
Original line number Diff line number Diff line
@@ -5848,8 +5848,6 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, 
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);

	}

}

arch/x86/kvm/mmu/tdp_mmu.c

+7 −15
Original line number Diff line number Diff line
@@ -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 @@ static bool zap_collapsible_spte_range(struct kvm *kvm, 
							    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 @@ static bool zap_collapsible_spte_range(struct kvm *kvm, 
			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);

}



/*

arch/x86/kvm/mmu/tdp_mmu.h

+2 −3
Original line number Diff line number Diff line
@@ -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,