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libc: Fall back to rdtsc when using pvclock and rdtscp is not available

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In preparation for a follow-up revision wherein kvmclock may export
timekeeping info to userspace even in the absence of AMDID_RDTSCP, fall
back to using rdtsc when rdtscp isn't available.  This mimics
pvclock_read_time_info() in the kernel.

Reviewed by:	kib
Tested by:	Shrikanth R Kamath <kshrikanth@juniper.net>
MFC after:	2 weeks
Sponsored by:	Klara, Inc.
Sponsored by:	Juniper Networks, Inc.
Differential Revision:	https://reviews.freebsd.org/D38341
This commit is contained in:
Mark Johnston 2023-02-03 10:53:20 -05:00
parent eb08932156
commit 26d105199e
1 changed files with 39 additions and 3 deletions
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42
lib/libc/x86/sys/__vdso_gettc.c
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@ -101,6 +101,13 @@ rdtsc32_mb_lfence(void)
return (rdtsc32());
}
static uint64_t
rdtsc_mb_lfence(void)
{
lfence();
return (rdtsc());
}
static u_int
rdtsc32_mb_mfence(void)
{
@ -108,38 +115,62 @@ rdtsc32_mb_mfence(void)
return (rdtsc32());
}
static uint64_t
rdtsc_mb_mfence(void)
{
mfence();
return (rdtsc());
}
static u_int
rdtsc32_mb_none(void)
{
return (rdtsc32());
}
static uint64_t
rdtsc_mb_none(void)
{
return (rdtsc());
}
static u_int
rdtscp32_(void)
{
return (rdtscp32());
}
static uint64_t
rdtscp_(void)
{
return (rdtscp());
}
struct tsc_selector_tag {
u_int (*ts_rdtsc32)(void);
uint64_t (*ts_rdtsc)(void);
u_int (*ts_rdtsc_low)(const struct vdso_timehands *);
};
static const struct tsc_selector_tag tsc_selector[] = {
[0] = { /* Intel, LFENCE */
.ts_rdtsc32 = rdtsc32_mb_lfence,
.ts_rdtsc = rdtsc_mb_lfence,
.ts_rdtsc_low = rdtsc_low_mb_lfence,
},
[1] = { /* AMD, MFENCE */
.ts_rdtsc32 = rdtsc32_mb_mfence,
.ts_rdtsc = rdtsc_mb_mfence,
.ts_rdtsc_low = rdtsc_low_mb_mfence,
},
[2] = { /* No SSE2 */
.ts_rdtsc32 = rdtsc32_mb_none,
.ts_rdtsc_low = rdtsc_low_mb_none,
.ts_rdtsc32 = rdtsc32_mb_none,
.ts_rdtsc = rdtsc_mb_none,
.ts_rdtsc_low = rdtsc_low_mb_none,
},
[3] = { /* RDTSCP */
.ts_rdtsc32 = rdtscp32_,
.ts_rdtsc = rdtscp_,
.ts_rdtsc_low = rdtscp_low,
},
};
@ -193,6 +224,11 @@ DEFINE_UIFUNC(static, u_int, __vdso_gettc_rdtsc32, (void))
return (tsc_selector[tsc_selector_idx(cpu_feature)].ts_rdtsc32);
}
DEFINE_UIFUNC(static, uint64_t, __vdso_gettc_rdtsc, (void))
{
return (tsc_selector[tsc_selector_idx(cpu_feature)].ts_rdtsc);
}
#define HPET_DEV_MAP_MAX 10
static volatile char *hpet_dev_map[HPET_DEV_MAP_MAX];
@ -325,7 +361,7 @@ __vdso_pvclock_gettc(const struct vdso_timehands *th, u_int *tc)
version = atomic_load_acq_32(&ti->version);
stable = (ti->flags & th->th_x86_pvc_stable_mask) != 0;
if (stable) {
tsc = rdtscp();
tsc = __vdso_gettc_rdtsc();
} else {
(void)rdtscp_aux(&cpuid_ti);
ti = &pvclock_timeinfos[cpuid_ti];