Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Tue, 13 Jul 2021 09:33:00 -0700
In-Reply-To: <20210713163324.627647-1-seanjc@google.com>
Message-Id: <20210713163324.627647-23-seanjc@google.com>
Mime-Version: 1.0
References: <20210713163324.627647-1-seanjc@google.com>
Subject: [PATCH v2 22/46] KVM: VMX: Remove direct write to vcpu->arch.cr0
 during vCPU RESET/INIT
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Reiji Watanabe <reijiw@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Remove a bogus write to vcpu->arch.cr0 that immediately precedes
vmx_set_cr0() during vCPU RESET/INIT.  For RESET, this is a nop since
the "old" CR0 value is meaningless.  But for INIT, if the vCPU is coming
from paging enabled mode, crushing vcpu->arch.cr0 will cause the various
is_paging() checks in vmx_set_cr0() to get false negatives.

For the exit_lmode() case, the false negative is benign as vmx_set_efer()
is called immediately after vmx_set_cr0().

For EPT without unrestricted guest, the false negative will cause KVM to
unnecessarily run with CR3 load/store exiting.  But again, this is
benign, albeit sub-optimal.

Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 02aec75ec6f6..ed631564c651 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4383,7 +4383,6 @@ static void init_vmcs(struct vcpu_vmx *vmx)
 static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
-	u64 cr0;
 
 	if (!init_event)
 		init_vmcs(vmx);
@@ -4454,9 +4453,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
 
-	cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
-	vmx->vcpu.arch.cr0 = cr0;
-	vmx_set_cr0(vcpu, cr0); /* enter rmode */
+	vmx_set_cr0(vcpu, X86_CR0_NW | X86_CR0_CD | X86_CR0_ET);
 	vmx_set_cr4(vcpu, 0);
 	vmx_set_efer(vcpu, 0);
 
-- 
2.32.0.93.g670b81a890-goog