Re: [PATCH v7 01/45] x86/compressed/64: detect/setup SEV/SME features earlier in boot

Venu Busireddy
2021-11-23T21:56:51Z

On 2021-11-12 14:30:01 -0600, Michael Roth wrote:
> On Fri, Nov 12, 2021 at 05:52:51PM +0100, Borislav Petkov wrote:
> > On Wed, Nov 10, 2021 at 04:06:47PM -0600, Brijesh Singh wrote:
> > > +void sev_enable(struct boot_params *bp)
> > > +{
> > > + unsigned int eax, ebx, ecx, edx;
> > > +
> > > + /* Check for the SME/SEV support leaf */
> > > + eax = 0x80000000;
> > > + ecx = 0;
> > > + native_cpuid(&eax, &ebx, &ecx, &edx);
> > > + if (eax < 0x8000001f)
> > > + return;
> > > +
> > > + /*
> > > + * Check for the SME/SEV feature:
> > > + * CPUID Fn8000_001F[EAX]
> > > + * - Bit 0 - Secure Memory Encryption support
> > > + * - Bit 1 - Secure Encrypted Virtualization support
> > > + * CPUID Fn8000_001F[EBX]
> > > + * - Bits 5:0 - Pagetable bit position used to indicate encryption
> > > + */
> > > + eax = 0x8000001f;
> > > + ecx = 0;
> > > + native_cpuid(&eax, &ebx, &ecx, &edx);
> > > + /* Check whether SEV is supported */
> > > + if (!(eax & BIT(1)))
> > > + return;
> > > +
> > > + /* Check the SEV MSR whether SEV or SME is enabled */
> > > + sev_status = rd_sev_status_msr();
> > > +
> > > + if (!(sev_status & MSR_AMD64_SEV_ENABLED))
> > > + error("SEV support indicated by CPUID, but not SEV status MSR.");
> >
> > What is the practical purpose of this test?
>
> In the current QEMU/KVM implementation the SEV* CPUID bits are only
> exposed for SEV guests, so this was more of a sanity check on that. But
> looking at things more closely: that's more of a VMM-specific behavior
> and isn't necessarily an invalid guest configuration as far as the spec
> is concerned, so I think this check should be dropped.
>
> >
> > > + sme_me_mask = 1UL << (ebx & 0x3f);
> >
> > sme_me_mask = BIT_ULL(ebx & 0x3f);
>
> Will do.

Also, could you please remove the references to set_sev_encryption_mask()
at lines 195 and 572? And perhaps reword those comments too?

Thanks,

Venu

> Thanks,
>
> Mike
>
> >
> > Thx.
> >
> > --
> > Regards/Gruss,
> > Boris.
> >
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