On Fri, Jan 15, 2021, Babu Moger wrote:
> ---
> arch/x86/include/asm/svm.h | 4 +++-
> arch/x86/kvm/svm/sev.c | 4 ++++
> arch/x86/kvm/svm/svm.c | 19 +++++++++++++++----
> 3 files changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 1c561945b426..772e60efe243 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -269,7 +269,9 @@ struct vmcb_save_area {
> * SEV-ES guests when referenced through the GHCB or for
> * saving to the host save area.
> */
> - u8 reserved_7[80];
> + u8 reserved_7[72];
> + u32 spec_ctrl; /* Guest version of SPEC_CTRL at 0x2E0 */
> + u8 reserved_7b[4];
Don't nested_prepare_vmcb_save() and nested_vmcb_checks() need to be updated to
handle the new field, too?
> u32 pkru;
> u8 reserved_7a[20];
> u64 reserved_8; /* rax already available at 0x01f8 */
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c8ffdbc81709..959d6e47bd84 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -546,6 +546,10 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
> save->pkru = svm->vcpu.arch.pkru;
> save->xss = svm->vcpu.arch.ia32_xss;
>
> + /* Update the guest SPEC_CTRL value in the save area */
> + if (boot_cpu_has(X86_FEATURE_V_SPEC_CTRL))
> + save->spec_ctrl = svm->spec_ctrl;
I think this can be dropped if svm->spec_ctrl is unused when V_SPEC_CTRL is
supported (see below). IIUC, the memcpy() that's just out of sight would do
the propgation to the VMSA.
> +
> /*
> * SEV-ES will use a VMSA that is pointed to by the VMCB, not
> * the traditional VMSA that is part of the VMCB. Copy the
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 7ef171790d02..a0cb01a5c8c5 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1244,6 +1244,9 @@ static void init_vmcb(struct vcpu_svm *svm)
>
> svm_check_invpcid(svm);
>
> + if (boot_cpu_has(X86_FEATURE_V_SPEC_CTRL))
> + save->spec_ctrl = svm->spec_ctrl;
> +
> if (kvm_vcpu_apicv_active(&svm->vcpu))
> avic_init_vmcb(svm);
>
> @@ -3789,7 +3792,10 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
> * is no need to worry about the conditional branch over the wrmsr
> * being speculatively taken.
> */
> - x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl);
> + if (static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
> + svm->vmcb->save.spec_ctrl = svm->spec_ctrl;
> + else
> + x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl);
Can't we avoid functional code in svm_vcpu_run() entirely when V_SPEC_CTRL is
supported? Make this code a nop, disable interception from time zero, and
read/write the VMBC field in svm_{get,set}_msr(). I.e. don't touch
svm->spec_ctrl if V_SPEC_CTRL is supported.
if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl);
svm_vcpu_enter_exit(vcpu, svm);
if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL) &&
unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
> svm_vcpu_enter_exit(vcpu, svm);
>
> @@ -3808,13 +3814,18 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
> * If the L02 MSR bitmap does not intercept the MSR, then we need to
> * save it.
> */
> - if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
> - svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
> + if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))) {
> + if (static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
> + svm->spec_ctrl = svm->vmcb->save.spec_ctrl;
> + else
> + svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
> + }
>
> if (!sev_es_guest(svm->vcpu.kvm))
> reload_tss(vcpu);
>
> - x86_spec_ctrl_restore_host(svm->spec_ctrl, svm->virt_spec_ctrl);
> + if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
> + x86_spec_ctrl_restore_host(svm->spec_ctrl, svm->virt_spec_ctrl);
>
> if (!sev_es_guest(svm->vcpu.kvm)) {
> vcpu->arch.cr2 = svm->vmcb->save.cr2;
>
