Re: [PATCH v8 01/40] x86/compressed/64: detect/setup SEV/SME features earlier in boot

Borislav Petkov
2021-12-10T19:13:00Z

On Fri, Dec 10, 2021 at 09:42:53AM -0600, Brijesh Singh wrote:
> @@ -447,6 +446,23 @@ SYM_CODE_START(startup_64)
> call load_stage1_idt
> popq %rsi
>
> +#ifdef CONFIG_AMD_MEM_ENCRYPT

I guess that ifdeffery is not needed.

> + /*
> + * Now that the stage1 interrupt handlers are set up, #VC exceptions from
> + * CPUID instructions can be properly handled for SEV-ES guests.
> + *
> + * For SEV-SNP, the CPUID table also needs to be set up in advance of any
> + * CPUID instructions being issued, so go ahead and do that now via
> + * sev_enable(), which will also handle the rest of the SEV-related
> + * detection/setup to ensure that has been done in advance of any dependent
> + * code.
> + */
> + pushq %rsi
> + movq %rsi, %rdi /* real mode address */
> + call sev_enable
> + popq %rsi
> +#endif
> +
> /*
> * paging_prepare() sets up the trampoline and checks if we need to
> * enable 5-level paging.

...

> +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;
> +
> + /* Set the SME mask if this is an SEV guest. */
> + sev_status = rd_sev_status_msr();
> +

^ Superfluous newline.

> + if (!(sev_status & MSR_AMD64_SEV_ENABLED))
> + return;
> +
> + sme_me_mask = BIT_ULL(ebx & 0x3f);
> +}
> --

Thx.

--
Regards/Gruss,
Boris.