linux-kernel - [PATCH] kvm: x86/mmu: Don't clear write flooding for direct SP

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Message-Id: <20230105100310.6700-1-jiangshanlai@gmail.com>
Date:   Thu,  5 Jan 2023 18:03:10 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org
Subject: [PATCH] kvm: x86/mmu: Don't clear write flooding for direct SP

From: Lai Jiangshan <jiangshan.ljs@...group.com>

Although there is no harm, but there is no point to clear write
flooding for direct SP.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 arch/x86/kvm/mmu/paging_tmpl.h | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 79da423ee4cb..11f17efbec97 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -649,12 +649,12 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 	if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root.hpa)))
 		goto out_gpte_changed;
 
-	for (shadow_walk_init(&it, vcpu, fault->addr);
-	     shadow_walk_okay(&it) && it.level > gw->level;
-	     shadow_walk_next(&it)) {
+	for_each_shadow_entry(vcpu, fault->addr, it) {
 		gfn_t table_gfn;
 
 		clear_sp_write_flooding_count(it.sptep);
+		if (it.level == gw->level)
+			break;
 
 		table_gfn = gw->table_gfn[it.level - 2];
 		access = gw->pt_access[it.level - 2];
@@ -706,8 +706,6 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 	trace_kvm_mmu_spte_requested(fault);
 
 	for (; shadow_walk_okay(&it); shadow_walk_next(&it)) {
-		clear_sp_write_flooding_count(it.sptep);
-
 		/*
 		 * We cannot overwrite existing page tables with an NX
 		 * large page, as the leaf could be executable.
-- 
2.19.1.6.gb485710b