[PATCH v10 17/24] x86/cc: Add CC_ATTR_GUEST_SECURE_TSC

[Nikunj A Dadhania <nikunj@amd.com>]

Add confidential compute platform attribute CC_ATTR_GUEST_SECURE_TSC that
can be used by the guest to query whether the Secure TSC feature is
active.

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
---
 include/linux/cc_platform.h | 8 ++++++++
 arch/x86/coco/core.c        | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index 60693a145894..57ec5c63277e 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -98,6 +98,14 @@ enum cc_attr {
 	 * enabled to run SEV-SNP guests.
 	 */
 	CC_ATTR_HOST_SEV_SNP,
+
+	/**
+	 * @CC_ATTR_GUEST_SECURE_TSC: Secure TSC is active.
+	 *
+	 * The platform/OS is running as a guest/virtual machine and actively
+	 * using AMD SEV-SNP Secure TSC feature.
+	 */
+	CC_ATTR_GUEST_SECURE_TSC,
 };
 
 #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index b31ef2424d19..df981e3ba80c 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -101,6 +101,9 @@ static bool noinstr amd_cc_platform_has(enum cc_attr attr)
 	case CC_ATTR_HOST_SEV_SNP:
 		return cc_flags.host_sev_snp;
 
+	case CC_ATTR_GUEST_SECURE_TSC:
+		return sev_status & MSR_AMD64_SNP_SECURE_TSC;
+
 	default:
 		return false;
 	}
-- 
2.34.1