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

[Borislav Petkov]

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?

> +	sme_me_mask = 1UL << (ebx & 0x3f);

	sme_me_mask = BIT_ULL(ebx & 0x3f);

Thx.

-- 
Regards/Gruss,
    Boris.

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