Re: [PATCH v16 05/13] x86/sev: Add Secure TSC support for SNP guests

Nikunj A. Dadhania
2025-01-08T07:47:29Z

On 1/8/2025 12:48 AM, Borislav Petkov wrote:
> On Tue, Jan 07, 2025 at 12:53:26PM -0600, Tom Lendacky wrote:
>> Yes, but from a readability point of view this makes it perfectly clear
>> that Secure TSC is only for SNP guests.
>
> That would mean that we need to check SNP with every SNP-specific feature
> which would be just silly. And all SNP feature bits have "SNP" in the same
> so...
>

Right, here is the updated diff:

diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index 715c2c09582f..d6647953590b 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -98,8 +98,7 @@ static bool noinstr amd_cc_platform_has(enum cc_attr attr)
return sev_status & MSR_AMD64_SEV_SNP_ENABLED;

case CC_ATTR_GUEST_SNP_SECURE_TSC:
- return (sev_status & MSR_AMD64_SEV_SNP_ENABLED) &&
- (sev_status & MSR_AMD64_SNP_SECURE_TSC);
+ return sev_status & MSR_AMD64_SNP_SECURE_TSC;

case CC_ATTR_HOST_SEV_SNP:
return cc_flags.host_sev_snp;
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 00a0ac3baab7..763cfeb65b2f 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -3218,7 +3218,8 @@ static int __init snp_get_tsc_info(void)

void __init snp_secure_tsc_prepare(void)
{
- if (!cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
+ if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP) ||
+ !cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
return;

if (snp_get_tsc_info()) {