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libc: vDSO timekeeping: Add pvclock support

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Add support for 'VDSO_TH_ALGO_X86_PVCLK'; add vDSO-based timekeeping for
devices that support the KVM/XEN paravirtual clock API.

Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
Reviewed by:	kib
Differential Revision:  https://reviews.freebsd.org/D31418
This commit is contained in:
Adam Fenn 2021-08-07 13:11:29 -07:00 committed by Konstantin Belousov
parent d4b2d3035a
commit a3d932dfef
1 changed files with 62 additions and 0 deletions
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62
lib/libc/x86/sys/__vdso_gettc.c
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@ -45,6 +45,7 @@ __FBSDID("$FreeBSD$");
#include "un-namespace.h"
#include <machine/atomic.h>
#include <machine/cpufunc.h>
#include <machine/pvclock.h>
#include <machine/specialreg.h>
#include <dev/acpica/acpi_hpet.h>
#ifdef WANT_HYPERV
@ -312,6 +313,61 @@ __vdso_hyperv_tsc(struct hyperv_reftsc *tsc_ref, u_int *tc)
#endif /* WANT_HYPERV */
static struct pvclock_vcpu_time_info *pvclock_timeinfos;
static int
__vdso_pvclock_gettc(const struct vdso_timehands *th, u_int *tc)
{
uint64_t delta, ns, tsc;
struct pvclock_vcpu_time_info *ti;
uint32_t cpuid_ti, cpuid_tsc, version;
bool stable;
do {
ti = &pvclock_timeinfos[0];
version = atomic_load_acq_32(&ti->version);
stable = (ti->flags & th->th_x86_pvc_stable_mask) != 0;
if (stable) {
tsc = rdtscp();
} else {
(void)rdtscp_aux(&cpuid_ti);
ti = &pvclock_timeinfos[cpuid_ti];
version = atomic_load_acq_32(&ti->version);
tsc = rdtscp_aux(&cpuid_tsc);
}
delta = tsc - ti->tsc_timestamp;
ns = ti->system_time + pvclock_scale_delta(delta,
ti->tsc_to_system_mul, ti->tsc_shift);
atomic_thread_fence_acq();
} while ((ti->version & 1) != 0 || ti->version != version ||
(!stable && cpuid_ti != cpuid_tsc));
*tc = MAX(ns, th->th_x86_pvc_last_systime);
return (0);
}
static void
__vdso_init_pvclock_timeinfos(void)
{
struct pvclock_vcpu_time_info *timeinfos;
size_t len;
int fd, ncpus;
unsigned int mode;
timeinfos = MAP_FAILED;
if (_elf_aux_info(AT_NCPUS, &ncpus, sizeof(ncpus)) != 0 ||
(cap_getmode(&mode) == 0 && mode != 0) ||
(fd = _open("/dev/" PVCLOCK_CDEVNAME, O_RDONLY | O_CLOEXEC)) < 0)
goto leave;
len = ncpus * sizeof(*pvclock_timeinfos);
timeinfos = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
_close(fd);
leave:
if (atomic_cmpset_rel_ptr(
(volatile uintptr_t *)&pvclock_timeinfos, (uintptr_t)NULL,
(uintptr_t)timeinfos) == 0 && timeinfos != MAP_FAILED)
(void)munmap((void *)timeinfos, len);
}
#pragma weak __vdso_gettc
int
__vdso_gettc(const struct vdso_timehands *th, u_int *tc)
@ -347,6 +403,12 @@ __vdso_gettc(const struct vdso_timehands *th, u_int *tc)
return (ENOSYS);
return (__vdso_hyperv_tsc(hyperv_ref_tsc, tc));
#endif
case VDSO_TH_ALGO_X86_PVCLK:
if (pvclock_timeinfos == NULL)
__vdso_init_pvclock_timeinfos();
if (pvclock_timeinfos == MAP_FAILED)
return (ENOSYS);
return (__vdso_pvclock_gettc(th, tc));
default:
return (ENOSYS);
}