[PATCH 1/5] KVM: pfncache: Snapshot mmu_invalidate_seq immediately before hva_to_pfn()

[Sean Christopherson]

Grab the snapshot of the mmu_notifier sequence counter immediately before
calling hva_to_pfn() when refreching a gpc, as there's no requirement that
the snapshot be taken while holding gpc->lock; the sequence counter is
completely independent of locking.  This will allow waiting on in-progress
invalidations to complete, instead of actively trying to resolve a pfn
that KVM is guaranteed to discard (because either the invalidation will
still be in-progress, or it will have completed and bumped the sequence
counter).

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 virt/kvm/pfncache.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index f0039efb9e1e..4afbc1262e3f 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -172,9 +172,6 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 	gpc->valid = false;
 
 	do {
-		mmu_seq = gpc->kvm->mmu_invalidate_seq;
-		smp_rmb();
-
 		write_unlock_irq(&gpc->lock);
 
 		/*
@@ -197,6 +194,9 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 			cond_resched();
 		}
 
+		mmu_seq = gpc->kvm->mmu_invalidate_seq;
+		smp_rmb();
+
 		/* We always request a writeable mapping */
 		new_pfn = hva_to_pfn(gpc->uhva, false, false, NULL, true, NULL);
 		if (is_error_noslot_pfn(new_pfn))

base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
-- 
2.47.0.rc1.288.g06298d1525-goog


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