[v15,09/13] tsc: Use the GUEST_TSC_FREQ MSR for discovering TSC frequency

Commit Message

Nikunj A. Dadhania Dec. 3, 2024, 9 a.m. UTC

Calibrating the TSC frequency using the kvmclock is not correct for
SecureTSC enabled guests. Use the platform provided TSC frequency via the
GUEST_TSC_FREQ MSR (C001_0134h).

Signed-off-by: Nikunj A Dadhania <[e-mail]>
---
 arch/x86/include/asm/sev.h |  2 ++
 arch/x86/coco/sev/core.c   | 16 ++++++++++++++++
 arch/x86/kernel/tsc.c      |  5 +++++
 3 files changed, 23 insertions(+)

Patch

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 9fd02efef08e..c4dca06b3b01 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -493,6 +493,7 @@  int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req
 			   struct snp_guest_request_ioctl *rio);
 
 void __init snp_secure_tsc_prepare(void);
+void __init snp_secure_tsc_init(void);
 
 #else	/* !CONFIG_AMD_MEM_ENCRYPT */
 
@@ -536,6 +537,7 @@  static inline void snp_msg_free(struct snp_msg_desc *mdesc) { }
 static inline int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
 					 struct snp_guest_request_ioctl *rio) { return -ENODEV; }
 static inline void __init snp_secure_tsc_prepare(void) { }
+static inline void __init snp_secure_tsc_init(void) { }
 
 #endif	/* CONFIG_AMD_MEM_ENCRYPT */
 
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 59c5e716fdd1..1bc668883058 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -3279,3 +3279,19 @@  void __init snp_secure_tsc_prepare(void)
 
 	pr_debug("SecureTSC enabled");
 }
+
+static unsigned long securetsc_get_tsc_khz(void)
+{
+	unsigned long long tsc_freq_mhz;
+
+	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
+	rdmsrl(MSR_AMD64_GUEST_TSC_FREQ, tsc_freq_mhz);
+
+	return (unsigned long)(tsc_freq_mhz * 1000);
+}
+
+void __init snp_secure_tsc_init(void)
+{
+	x86_platform.calibrate_cpu = securetsc_get_tsc_khz;
+	x86_platform.calibrate_tsc = securetsc_get_tsc_khz;
+}
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 67aeaba4ba9c..c0eef924b84e 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -30,6 +30,7 @@ 
 #include <asm/i8259.h>
 #include <asm/topology.h>
 #include <asm/uv/uv.h>
+#include <asm/sev.h>
 
 unsigned int __read_mostly cpu_khz;	/* TSC clocks / usec, not used here */
 EXPORT_SYMBOL(cpu_khz);
@@ -1515,6 +1516,10 @@  void __init tsc_early_init(void)
 	/* Don't change UV TSC multi-chassis synchronization */
 	if (is_early_uv_system())
 		return;
+
+	if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
+		snp_secure_tsc_init();
+
 	if (!determine_cpu_tsc_frequencies(true))
 		return;
 	tsc_enable_sched_clock();