linux-kernel - [RFC PATCH 26/35] KVM: SVM: Guest FPU state save/restore not needed for SEV-ES guest

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Message-Id: <ac35a419e395d355d86f3b44ce219dc63864db00.1600114548.git.thomas.lendacky@amd.com>
Date:   Mon, 14 Sep 2020 15:15:40 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: [RFC PATCH 26/35] KVM: SVM: Guest FPU state save/restore not needed for SEV-ES guest

From: Tom Lendacky <thomas.lendacky@....com>

The guest FPU is automatically restored on VMRUN and saved on VMEXIT by
the hardware, so there is no reason to do this in KVM.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/kvm/svm/svm.c |  8 ++++++--
 arch/x86/kvm/x86.c     | 18 ++++++++++++++----
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b35c2de1130c..48699c41b62a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3682,7 +3682,9 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 		svm_set_dr6(svm, DR6_FIXED_1 | DR6_RTM);
 
 	clgi();
-	kvm_load_guest_xsave_state(vcpu);
+
+	if (!sev_es_guest(svm->vcpu.kvm))
+		kvm_load_guest_xsave_state(vcpu);
 
 	if (lapic_in_kernel(vcpu) &&
 		vcpu->arch.apic->lapic_timer.timer_advance_ns)
@@ -3728,7 +3730,9 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 	if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
 		kvm_before_interrupt(&svm->vcpu);
 
-	kvm_load_host_xsave_state(vcpu);
+	if (!sev_es_guest(svm->vcpu.kvm))
+		kvm_load_host_xsave_state(vcpu);
+
 	stgi();
 
 	/* Any pending NMI will happen here */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 76efe70cd635..a53e24c1c5d1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8896,9 +8896,14 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
 
 	kvm_save_current_fpu(vcpu->arch.user_fpu);
 
-	/* PKRU is separately restored in kvm_x86_ops.run.  */
-	__copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,
-				~XFEATURE_MASK_PKRU);
+	/*
+	 * An encrypted save area means that the guest state can't be
+	 * set by the hypervisor, so skip trying to set it.
+	 */
+	if (!vcpu->arch.vmsa_encrypted)
+		/* PKRU is separately restored in kvm_x86_ops.run. */
+		__copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,
+					~XFEATURE_MASK_PKRU);
 
 	fpregs_mark_activate();
 	fpregs_unlock();
@@ -8911,7 +8916,12 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 {
 	fpregs_lock();
 
-	kvm_save_current_fpu(vcpu->arch.guest_fpu);
+	/*
+	 * An encrypted save area means that the guest state can't be
+	 * read/saved by the hypervisor, so skip trying to save it.
+	 */
+	if (!vcpu->arch.vmsa_encrypted)
+		kvm_save_current_fpu(vcpu->arch.guest_fpu);
 
 	copy_kernel_to_fpregs(&vcpu->arch.user_fpu->state);
 
-- 
2.28.0