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:

quoted

+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.

quoted

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

	sme_me_mask = BIT_ULL(ebx & 0x3f);

Will do.

Thanks,

Mike

Thx.

-- 
Regards/Gruss,
    Boris.

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