Merge tag 'x86_urgent_for_v6.16_rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fix from Borislav Petkov:

 - Make sure AMD SEV guests using secure TSC, include a TSC_FACTOR which
   prevents their TSCs from going skewed from the hypervisor's

* tag 'x86_urgent_for_v6.16_rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation

Author: torvalds

arch/x86/coco/sev/core.c

@@ -88,7 +88,7 @@ static const char * const sev_status_feat_names[] = {
  */
 static u64 snp_tsc_scale __ro_after_init;
 static u64 snp_tsc_offset __ro_after_init;
-static u64 snp_tsc_freq_khz __ro_after_init;
+static unsigned long snp_tsc_freq_khz __ro_after_init;
 
 DEFINE_PER_CPU(struct sev_es_runtime_data*, runtime_data);
 DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
@@ -2167,15 +2167,31 @@ static unsigned long securetsc_get_tsc_khz(void)
 
 void __init snp_secure_tsc_init(void)
 {
-	unsigned long long tsc_freq_mhz;
+	struct snp_secrets_page *secrets;
+	unsigned long tsc_freq_mhz;
+	void *mem;
 
 	if (!cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
 		return;
 
+	mem = early_memremap_encrypted(sev_secrets_pa, PAGE_SIZE);
+	if (!mem) {
+		pr_err("Unable to get TSC_FACTOR: failed to map the SNP secrets page.\n");
+		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SECURE_TSC);
+	}
+
+	secrets = (__force struct snp_secrets_page *)mem;
+
 	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 	rdmsrq(MSR_AMD64_GUEST_TSC_FREQ, tsc_freq_mhz);
-	snp_tsc_freq_khz = (unsigned long)(tsc_freq_mhz * 1000);
+
+	/* Extract the GUEST TSC MHZ from BIT[17:0], rest is reserved space */
+	tsc_freq_mhz &= GENMASK_ULL(17, 0);
+
+	snp_tsc_freq_khz = SNP_SCALE_TSC_FREQ(tsc_freq_mhz * 1000, secrets->tsc_factor);
 
 	x86_platform.calibrate_cpu = securetsc_get_tsc_khz;
 	x86_platform.calibrate_tsc = securetsc_get_tsc_khz;
+
+	early_memunmap(mem, PAGE_SIZE);
 }

arch/x86/include/asm/sev.h

@@ -223,6 +223,18 @@ struct snp_tsc_info_resp {
 	u8 rsvd2[100];
 } __packed;
 
+/*
+ * Obtain the mean TSC frequency by decreasing the nominal TSC frequency with
+ * TSC_FACTOR as documented in the SNP Firmware ABI specification:
+ *
+ * GUEST_TSC_FREQ * (1 - (TSC_FACTOR * 0.00001))
+ *
+ * which is equivalent to:
+ *
+ * GUEST_TSC_FREQ -= (GUEST_TSC_FREQ * TSC_FACTOR) / 100000;
+ */
+#define SNP_SCALE_TSC_FREQ(freq, factor) ((freq) - (freq) * (factor) / 100000)
+
 struct snp_guest_req {
 	void *req_buf;
 	size_t req_sz;
@@ -282,8 +294,11 @@ struct snp_secrets_page {
 	u8 svsm_guest_vmpl;
 	u8 rsvd3[3];
 
+	/* The percentage decrease from nominal to mean TSC frequency. */
+	u32 tsc_factor;
+
 	/* Remainder of page */
-	u8 rsvd4[3744];
+	u8 rsvd4[3740];
 } __packed;
 
 struct snp_msg_desc {