linux-kernel - [PATCH v3 1/8] Revert "KVM: Do not speculatively mark pfn cache valid to "fix" race"

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Message-Id: <20220429210025.3293691-2-seanjc@google.com>
Date:   Fri, 29 Apr 2022 21:00:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH v3 1/8] Revert "KVM: Do not speculatively mark pfn cache valid
 to "fix" race"

This reverts commit 55111927df1cd140aa7b7ea3f33f524b87776381.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/pfncache.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 72eee096a7cd..71c84a43024c 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -81,8 +81,6 @@ bool kvm_gfn_to_pfn_cache_check(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
 {
 	struct kvm_memslots *slots = kvm_memslots(kvm);
 
-	lockdep_assert_held_read(&gpc->lock);
-
 	if ((gpa & ~PAGE_MASK) + len > PAGE_SIZE)
 		return false;
 
@@ -228,6 +226,11 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
 	if (!old_valid || old_uhva != gpc->uhva) {
 		void *new_khva = NULL;
 
+		/* Placeholders for "hva is valid but not yet mapped" */
+		gpc->pfn = KVM_PFN_ERR_FAULT;
+		gpc->khva = NULL;
+		gpc->valid = true;
+
 		new_pfn = hva_to_pfn_retry(kvm, gpc);
 		if (is_error_noslot_pfn(new_pfn)) {
 			ret = -EFAULT;
@@ -256,7 +259,7 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
 			gpc->pfn = KVM_PFN_ERR_FAULT;
 			gpc->khva = NULL;
 		} else {
-			gpc->valid = true;
+			/* At this point, gpc->valid may already have been cleared */
 			gpc->pfn = new_pfn;
 			gpc->khva = new_khva;
 		}
-- 
2.36.0.464.gb9c8b46e94-goog