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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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