linux-kernel - [PATCH 7/7] KVM: X86: Also prefetch the last range in __direct_pte

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Date:   Tue, 24 Aug 2021 15:55:23 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org
Subject: [PATCH 7/7] KVM: X86: Also prefetch the last range in __direct_pte_prefetch().

From: Lai Jiangshan <laijs@...ux.alibaba.com>

__direct_pte_prefetch() skips prefetching the last range.

The last range are often the whole range after the faulted spte when
guest is touching huge-page-mapped(in guest view) memory forwardly
which means prefetching them can reduce pagefault.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/kvm/mmu/mmu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e5932af6f11c..ac260e01e9d8 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2847,8 +2847,9 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
 	i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1);
 	spte = sp->spt + i;
 
-	for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
-		if (is_shadow_present_pte(*spte) || spte == sptep) {
+	for (i = 0; i <= PTE_PREFETCH_NUM; i++, spte++) {
+		if (i == PTE_PREFETCH_NUM ||
+		    is_shadow_present_pte(*spte) || spte == sptep) {
 			if (!start)
 				continue;
 			if (direct_pte_prefetch_many(vcpu, sp, start, spte) < 0)
-- 
2.19.1.6.gb485710b