linux-kernel - [PATCH v6 17/17] KVM: x86: nSVM: optimize svm_set_x2apic_msr

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Date:   Thu, 19 May 2022 05:27:09 -0500
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
CC:     <pbonzini@...hat.com>, <mlevitsk@...hat.com>, <seanjc@...gle.com>,
        <joro@...tes.org>, <jon.grimm@....com>, <wei.huang2@....com>,
        <terry.bowman@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [PATCH v6 17/17] KVM: x86: nSVM: optimize svm_set_x2apic_msr_interception

From: Maxim Levitsky <mlevitsk@...hat.com>

- Avoid toggling the x2apic msr interception if it is already up to date.

- Avoid touching L0 msr bitmap when AVIC is inhibited on entry to
  the guest mode, because in this case the guest usually uses its
  own msr bitmap.

  Later on VM exit, the 1st optimization will allow KVM to skip
  touching the L0 msr bitmap as well.

Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/avic.c | 8 ++++++++
 arch/x86/kvm/svm/svm.c  | 7 +++++++
 arch/x86/kvm/svm/svm.h  | 2 ++
 3 files changed, 17 insertions(+)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 2a9eb419bdb9..0d7499678cb9 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -100,6 +100,14 @@ static void avic_deactivate_vmcb(struct vcpu_svm *svm)
 	vmcb->control.int_ctl &= ~(AVIC_ENABLE_MASK | X2APIC_MODE_MASK);
 	vmcb->control.avic_physical_id &= ~AVIC_PHYSICAL_MAX_INDEX_MASK;
 
+	/*
+	 * If running nested and the guest uses its own MSR bitmap, there
+	 * is no need to update L0's msr bitmap
+	 */
+	if (is_guest_mode(&svm->vcpu) &&
+	    vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT))
+		return;
+
 	/* Enabling MSR intercept for x2APIC registers */
 	svm_set_x2apic_msr_interception(svm, true);
 }
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e04a133b98d0..4165317c0b00 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -750,6 +750,9 @@ void svm_set_x2apic_msr_interception(struct vcpu_svm *svm, bool intercept)
 {
 	int i;
 
+	if (intercept == svm->x2avic_msrs_intercepted)
+		return;
+
 	if (avic_mode != AVIC_MODE_X2 ||
 	    !apic_x2apic_mode(svm->vcpu.arch.apic))
 		return;
@@ -763,6 +766,8 @@ void svm_set_x2apic_msr_interception(struct vcpu_svm *svm, bool intercept)
 		set_msr_interception(&svm->vcpu, svm->msrpm, index,
 				     !intercept, !intercept);
 	}
+
+	svm->x2avic_msrs_intercepted = intercept;
 }
 
 void svm_vcpu_free_msrpm(u32 *msrpm)
@@ -1333,6 +1338,8 @@ static int svm_vcpu_create(struct kvm_vcpu *vcpu)
 		goto error_free_vmsa_page;
 	}
 
+	svm->x2avic_msrs_intercepted = true;
+
 	svm->vmcb01.ptr = page_address(vmcb01_page);
 	svm->vmcb01.pa = __sme_set(page_to_pfn(vmcb01_page) << PAGE_SHIFT);
 	svm_switch_vmcb(svm, &svm->vmcb01);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 309445619756..6395b7791f26 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -272,6 +272,8 @@ struct vcpu_svm {
 	struct vcpu_sev_es_state sev_es;
 
 	bool guest_state_loaded;
+
+	bool x2avic_msrs_intercepted;
 };
 
 struct svm_cpu_data {
-- 
2.25.1