Re: [PATCH v8 29/40] x86/compressed/64: add support for SEV-SNP CPUID table in #VC handlers

Borislav Petkov
2022-01-18T14:02:53Z

On Mon, Jan 17, 2022 at 10:35:21PM -0600, Michael Roth wrote:
> Unfortunately, in sev_enable(), between the point where snp_init() is
> called, and sev_status is actually set, there are a number of cpuid
> intructions which will make use of do_vc_no_ghcb() prior to sev_status
> being set (and it needs to happen in that order to set sev_status
> appropriately). After that point, snp_cpuid_active() would no longer be
> necessary, but during that span some indicator is needed in case this
> is just an SEV-ES guest trigger cpuid #VCs.

You mean testing what snp_cpuid_info_create() set up is not enough?

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 7bc7e297f88c..17cfe804bad3 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -523,7 +523,9 @@ static int snp_cpuid_postprocess(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
static int snp_cpuid(u32 func, u32 subfunc, u32 *eax, u32 *ebx, u32 *ecx,
u32 *edx)
{
- if (!snp_cpuid_active())
+ const struct snp_cpuid_info *c = snp_cpuid_info_get_ptr();
+
+ if (!c->count)
return -EOPNOTSUPP;

if (!snp_cpuid_find_validated_func(func, subfunc, eax, ebx, ecx, edx)) {

---

Btw, all those

/* SEV-SNP CPUID table should be set up now. */
if (!snp_cpuid_active())
sev_es_terminate(1, GHCB_TERM_CPUID);

after snp_cpuid_info_create() has returned are useless either. If that
function returns, you know you're good to go wrt SNP.

Thx.

--
Regards/Gruss,
Boris.