linux-kernel - [PATCH v3 4/8] KVM: Put the extra pfn reference when reusing a pfn in the gpc cache

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Message-Id: <20220429210025.3293691-5-seanjc@google.com>
Date:   Fri, 29 Apr 2022 21:00:21 +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 4/8] KVM: Put the extra pfn reference when reusing a pfn in
 the gpc cache

Put the struct page reference to pfn acquired by hva_to_pfn() when the
old and new pfns for a gfn=>pfn cache match.  The cache already has a
reference via the old/current pfn, and will only put one reference when
the cache is done with the pfn.

Fixes: 982ed0de4753 ("KVM: Reinstate gfn_to_pfn_cache with invalidation support")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/pfncache.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index e05a6a1b8eff..40cbe90d52e0 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -206,6 +206,14 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
 
 		if (gpc->usage & KVM_HOST_USES_PFN) {
 			if (new_pfn == old_pfn) {
+				/*
+				 * Reuse the existing pfn and khva, but put the
+				 * reference acquired hva_to_pfn_retry(); the
+				 * cache still holds a reference to the pfn
+				 * from the previous refresh.
+				 */
+				gpc_release_pfn_and_khva(kvm, new_pfn, NULL);
+
 				new_khva = old_khva;
 				old_pfn = KVM_PFN_ERR_FAULT;
 				old_khva = NULL;
-- 
2.36.0.464.gb9c8b46e94-goog