linux-kernel - [v2 PATCH] x86/kvm/mmu: Remove unnecessary ‘NULL’ values from sptep

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Message-Id: <20230905182006.2964-1-zeming@nfschina.com>
Date:   Wed,  6 Sep 2023 02:20:06 +0800
From:   Li zeming <zeming@...china.com>
To:     seanjc@...gle.com, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Li zeming <zeming@...china.com>
Subject: [v2 PATCH] x86/kvm/mmu: Remove unnecessary ‘NULL’ values from sptep

Remove spte and sptep initialization assignments, add sptep assignment
check and processing.

Signed-off-by: Li zeming <zeming@...china.com>
---
 v2:
   1. Remove spte initialization assignment.
   2. Add sptep assignment check.

 arch/x86/kvm/mmu/mmu.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index ec169f5c7dce..0d11bfeae2f8 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3456,8 +3456,8 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 {
 	struct kvm_mmu_page *sp;
 	int ret = RET_PF_INVALID;
-	u64 spte = 0ull;
-	u64 *sptep = NULL;
+	u64 spte;
+	u64 *sptep;
 	uint retry_count = 0;
 
 	if (!page_fault_can_be_fast(fault))
@@ -3473,6 +3473,14 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 		else
 			sptep = fast_pf_get_last_sptep(vcpu, fault->addr, &spte);
 
+		/*
+		 * It's entirely possible for the mapping to have been zapped
+		 * by a different task, but the root page is should always be
+		 * available as the vCPU holds a reference to its root(s).
+		 */
+		if (WARN_ON_ONCE(!sptep))
+			spte = REMOVED_SPTE;
+
 		if (!is_shadow_present_pte(spte))
 			break;
 
-- 
2.18.2