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

Thanks,

Mike

>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpeople.kernel.org%2Ftglx%2Fnotes-about-netiquette&amp;data=04%7C01%7Cmichael.roth%40amd.com%7Ca6bf3479fffa4b5eee8b08d9a5fce2e2%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637723327924654730%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=SRy8YSe8a2njNc6IT8CGKv0hUefSOW55DJV%2Fi2Lhkic%3D&amp;reserved=0

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