On Thu, Nov 02, 2023 at 08:07:20PM +0200, Maxim Levitsky wrote:
> On Tue, 2023-10-10 at 20:02 +0000, John Allen wrote:
> > When running as an SEV-ES guest, the PL0_SSP, PL1_SSP, PL2_SSP, PL3_SSP,
> > and U_CET fields in the VMCB save area are type B, meaning the host
> > state is automatically loaded on a VMEXIT, but is not saved on a VMRUN.
> > The other shadow stack MSRs, S_CET, SSP, and ISST_ADDR are type A,
> > meaning they are loaded on VMEXIT and saved on VMRUN. PL0_SSP, PL1_SSP,
> > and PL2_SSP are currently unused. Manually save the other type B host
> > MSR values before VMRUN.
> >
> > Signed-off-by: John Allen <john.allen@xxxxxxx>
> > ---
> > arch/x86/kvm/svm/sev.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index b9a0a939d59f..bb4b18baa6f7 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -3098,6 +3098,15 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa)
> > hostsa->dr2_addr_mask = amd_get_dr_addr_mask(2);
> > hostsa->dr3_addr_mask = amd_get_dr_addr_mask(3);
> > }
> > +
> > + if (boot_cpu_has(X86_FEATURE_SHSTK)) {
> > + /*
> > + * MSR_IA32_U_CET and MSR_IA32_PL3_SSP are restored on VMEXIT,
> > + * save the current host values.
> > + */
> > + rdmsrl(MSR_IA32_U_CET, hostsa->u_cet);
> > + rdmsrl(MSR_IA32_PL3_SSP, hostsa->pl3_ssp);
> > + }
> > }
>
>
> Do we actually need this patch?
>
> Host FPU state is not encrypted, and as far as I understood from the common CET patch series,
> that on return to userspace these msrs will be restored.
Hi Maxim,
I think you're right on this. My next version omits the patch and
testing seems to confirm that it's not needed.
>
> Best regards,
> Maxim Levitsky
>
>
> PS: AMD's APM is silent on how 'S_CET, SSP, and ISST_ADDR' are saved/restored for non encrypted guests.
> Are they also type A?
>
> Can the VMSA table be trusted in general to provide the same swap type as for the non encrypted guests?
>From what I gather, for a non-SEV-ES guest using the save area that is part
of the VMCB as opposed to the separate VMCB/VMSA for SEV-ES and SEV-SNP,
anything listed in that save area will effectively be swap type A. Does that
answer your question?
Thanks,
John
>
>
> >
> > void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
>
>
