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Subject[RFC PATCH 26/35] KVM: SVM: Guest FPU state save/restore not needed for SEV-ES guest
Date
From: Tom Lendacky <thomas.lendacky@amd.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@amd.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
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