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

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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
This commit is contained in:
Linus Torvalds
2025-07-06 10:44:20 -07:00
parent 463b1b2af8 52e1a03e6c
commit 5fc2e891a5
2 changed files with 35 additions and 4 deletions
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arch/x86/coco/sev/core.c
+19 -3
View File
@@ -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
+16 -1
View File
@@ -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 {