linux-kernel - [RFC PATCH 1/6] KVM: X86: Check root_level only in fast_pgd

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Message-Id: <20211210092508.7185-2-jiangshanlai@gmail.com>
Date:   Fri, 10 Dec 2021 17:25:03 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.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>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [RFC PATCH 1/6] KVM: X86: Check root_level only in fast_pgd_switch()

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

If root_level >= 4, shadow_root_level must be >= 4 too.
Checking only root_level can reduce a check.

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

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 11b06d536cc9..846a2e426e0b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4136,8 +4136,7 @@ static bool fast_pgd_switch(struct kvm_vcpu *vcpu, gpa_t new_pgd,
 	 * having to deal with PDPTEs. We may add support for 32-bit hosts/VMs
 	 * later if necessary.
 	 */
-	if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL &&
-	    mmu->root_level >= PT64_ROOT_4LEVEL)
+	if (mmu->root_level >= PT64_ROOT_4LEVEL)
 		return cached_root_available(vcpu, new_pgd, new_role);
 
 	return false;
-- 
2.19.1.6.gb485710b