linux-kernel - [PATCH 10/15] KVM: X86: Skip allocating pae_root for vcpu->arch.guest_mmu when !tdp

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Message-Id: <20211118110814.2568-11-jiangshanlai@gmail.com>
Date:   Thu, 18 Nov 2021 19:08:09 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     kvm@...r.kernel.org, Lai Jiangshan <laijs@...ux.alibaba.com>,
        Paolo Bonzini <pbonzini@...hat.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>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 10/15] KVM: X86: Skip allocating pae_root for vcpu->arch.guest_mmu when !tdp_enabled

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

It is never used.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/kvm/mmu/mmu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8f0035517450..e1fe8af874ef 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5501,6 +5501,10 @@ static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
 	for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
 		mmu->prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;
 
+	/* vcpu->arch.guest_mmu isn't used when !tdp_enabled. */
+	if (!tdp_enabled && mmu == &vcpu->arch.guest_mmu)
+		return 0;
+
 	/*
 	 * When using PAE paging, the four PDPTEs are treated as 'root' pages,
 	 * while the PDP table is a per-vCPU construct that's allocated at MMU
-- 
2.19.1.6.gb485710b