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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.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,
	Reto Buerki <reet@codelabs.ch>,
	Liran Alon <liran.alon@oracle.com>
Subject: [PATCH v2 2/8] KVM: VMX: Skip GUEST_CR3 VMREAD+VMWRITE if the VMCS is up-to-date
Date: Fri, 27 Sep 2019 14:45:17 -0700	[thread overview]
Message-ID: <20190927214523.3376-3-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20190927214523.3376-1-sean.j.christopherson@intel.com>

Skip the VMWRITE to update GUEST_CR3 if CR3 is not available, i.e. has
not been read from the VMCS since the last VM-Enter.  If vcpu->arch.cr3
is stale, kvm_read_cr3(vcpu) will refresh vcpu->arch.cr3 from the VMCS,
meaning KVM will do a VMREAD and then VMWRITE the value it just pulled
from the VMCS.

Note, this is a purely theoretical change, no instances of skipping
the VMREAD+VMWRITE have been observed with this change.

Tested-by: Reto Buerki <reet@codelabs.ch>
Tested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/vmx/vmx.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7679c2a05a50..0b8dd9c315f8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3004,10 +3004,12 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 		/* Loading vmcs02.GUEST_CR3 is handled by nested VM-Enter. */
 		if (is_guest_mode(vcpu))
 			update_guest_cr3 = false;
-		else if (enable_unrestricted_guest || is_paging(vcpu))
-			guest_cr3 = kvm_read_cr3(vcpu);
-		else
+		else if (!enable_unrestricted_guest && !is_paging(vcpu))
 			guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr;
+		else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
+			guest_cr3 = vcpu->arch.cr3;
+		else /* vmcs01.GUEST_CR3 is already up-to-date. */
+			update_guest_cr3 = false;
 		ept_load_pdptrs(vcpu);
 	}
 
-- 
2.22.0


  parent reply	other threads:[~2019-09-27 21:45 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-27 21:45 [PATCH v2 0/8] KVM: x86: nVMX GUEST_CR3 bug fix, and then some Sean Christopherson
2019-09-27 21:45 ` [PATCH v2 1/8] KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter Sean Christopherson
2019-09-27 23:37   ` Jim Mattson
2019-09-27 21:45 ` Sean Christopherson [this message]
2019-09-27 21:45 ` [PATCH v2 3/8] KVM: VMX: Consolidate to_vmx() usage in RFLAGS accessors Sean Christopherson
2019-09-30  8:48   ` Vitaly Kuznetsov
2019-09-27 21:45 ` [PATCH v2 4/8] KVM: VMX: Optimize vmx_set_rflags() for unrestricted guest Sean Christopherson
2019-09-30  8:57   ` Vitaly Kuznetsov
2019-09-30 15:19     ` Sean Christopherson
2019-09-30 15:55       ` Vitaly Kuznetsov
2019-10-09 10:40   ` Paolo Bonzini
2019-10-09 16:38     ` Sean Christopherson
2019-10-09 20:59       ` Paolo Bonzini
2019-10-09 21:30         ` Sean Christopherson
2019-09-27 21:45 ` [PATCH v2 5/8] KVM: x86: Add WARNs to detect out-of-bounds register indices Sean Christopherson
2019-09-30  9:19   ` Vitaly Kuznetsov
2019-10-09 10:50   ` Paolo Bonzini
2019-10-09 16:36     ` Sean Christopherson
2019-09-27 21:45 ` [PATCH v2 6/8] KVM: x86: Fold 'enum kvm_ex_reg' definitions into 'enum kvm_reg' Sean Christopherson
2019-09-30  9:25   ` Vitaly Kuznetsov
2019-10-09 10:52     ` Paolo Bonzini
2019-10-09 11:27       ` Vitaly Kuznetsov
2019-09-27 21:45 ` [PATCH v2 7/8] KVM: x86: Add helpers to test/mark reg availability and dirtiness Sean Christopherson
2019-09-30  9:32   ` Vitaly Kuznetsov
2019-10-09 11:00     ` Paolo Bonzini
2019-09-27 21:45 ` [PATCH v2 8/8] KVM: x86: Fold decache_cr3() into cache_reg() Sean Christopherson
2019-09-30 10:58   ` Vitaly Kuznetsov
2019-09-30 15:04     ` Sean Christopherson
2019-09-30 15:27       ` Vitaly Kuznetsov
2019-09-30 15:33         ` Sean Christopherson
2019-10-09 11:03   ` Paolo Bonzini
2019-09-30 10:42 ` [PATCH v2 0/8] KVM: x86: nVMX GUEST_CR3 bug fix, and then some Reto Buerki
2019-10-29 15:03   ` Martin Lucina
2019-10-30  9:09     ` Sean Christopherson

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