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x86/tsc: Init the TSC for Secure TSC guests

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Use the GUEST_TSC_FREQ MSR to discover the TSC frequency instead of
relying on kvm-clock based frequency calibration.  Override both CPU and
TSC frequency calibration callbacks with securetsc_get_tsc_khz(). Since
the difference between CPU base and TSC frequency does not apply in this
case, the same callback is being used.

  [ bp: Carve out from
    https://lore.kernel.org/r/20250106124633.1418972-11-nikunj@amd.com ]

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250106124633.1418972-11-nikunj@amd.com
This commit is contained in:
Nikunj A Dadhania 2025-01-06 18:16:30 +05:30 committed by Borislav Petkov (AMD)
parent 0a2a98f691
commit 73bbf3b0fb
3 changed files with 27 additions and 0 deletions
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21
arch/x86/coco/sev/core.c
View file

@ -103,6 +103,7 @@ static u64 secrets_pa __ro_after_init;
*/
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;
/* #VC handler runtime per-CPU data */
struct sev_es_runtime_data {
@ -3278,3 +3279,23 @@ void __init snp_secure_tsc_prepare(void)
pr_debug("SecureTSC enabled");
}
static unsigned long securetsc_get_tsc_khz(void)
{
return snp_tsc_freq_khz;
}
void __init snp_secure_tsc_init(void)
{
unsigned long long tsc_freq_mhz;
if (!cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
return;
setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
rdmsrl(MSR_AMD64_GUEST_TSC_FREQ, tsc_freq_mhz);
snp_tsc_freq_khz = (unsigned long)(tsc_freq_mhz * 1000);
x86_platform.calibrate_cpu = securetsc_get_tsc_khz;
x86_platform.calibrate_tsc = securetsc_get_tsc_khz;
}

2
arch/x86/include/asm/sev.h
View file

@ -482,6 +482,7 @@ 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 */
@ -524,6 +525,7 @@ 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 */

4
arch/x86/kernel/tsc.c
View file

@ -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 +1516,9 @@ void __init tsc_early_init(void)
/* Don't change UV TSC multi-chassis synchronization */
if (is_early_uv_system())
return;
snp_secure_tsc_init();
if (!determine_cpu_tsc_frequencies(true))
return;
tsc_enable_sched_clock();