Commit 8d73829b authored by Tom Lendacky's avatar Tom Lendacky Committed by Borislav Petkov (AMD)
Browse files

x86/startup/sev: Document the CPUID flow in the boot #VC handler 



Document the CPUID reading the different SEV guest types do - the SNP
one which relies on the presence of a CPUID table and the SEV-ES one,
which reads the CPUID supplied by the hypervisor.

The intent being to clarify the two back-to-back, similar CPUID
invocations.

No functional changes.

  [ bp: Turn into a proper patch. ]

Signed-off-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/fbb24767-0e06-d1d6-36e0-1757d98aca66@amd.com
parent 26a9f90b

arch/x86/boot/startup/sev-shared.c

+11 −0
Original line number Diff line number Diff line
@@ -458,6 +458,13 @@ void do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code) 
	leaf.fn = fn;

	leaf.subfn = subfn;



	/*

	 * If SNP is active, then snp_cpuid() uses the CPUID table to obtain the

	 * CPUID values (with possible HV interaction during post-processing of

	 * the values). But if SNP is not active (no CPUID table present), then

	 * snp_cpuid() returns -EOPNOTSUPP so that an SEV-ES guest can call the

	 * HV to obtain the CPUID information.

	 */

	ret = snp_cpuid(snp_cpuid_hv_msr, NULL, &leaf);

	if (!ret)

		goto cpuid_done;
@@ -465,6 +472,10 @@ void do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code) 
	if (ret != -EOPNOTSUPP)

		goto fail;



	/*

	 * This is reached by a SEV-ES guest and needs to invoke the HV for

	 * the CPUID data.

	 */

	if (__sev_cpuid_hv_msr(&leaf))

		goto fail;