On 1/19/21 12:31 PM, Sean Christopherson wrote:
> 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?
Ok. Sure. I will check and test few combinations to make sure of these
changes.
>
>> 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.
Yes, That is right. I will remove this.
>
>> +
>> /*
>> * 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
Sean, I thought you mentioned earlier about not changing the interception
mechanism. Do you think we should disable the interception right away if
V_SPEC_CTRL is supported?
> 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);
Ok. It appears the above code might work fine with changes in
svm_{get,set}_msr() to update save spec_ctlr. I will retest few
combinations to make sure it works.
Thanks
Babu
>
>> 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;
>>
