blob: 34eef083c9882fafbd3bf5cc25a0dd5fdb38b06d [file] [log] [blame]
/* SPDX-License-Identifier: GPL-2.0 */
* Definitions for the clocksource provided by the Hyper-V
* hypervisor to guest VMs, as described in the Hyper-V Top
* Level Functional Spec (TLFS).
* Copyright (C) 2019, Microsoft, Inc.
* Author: Michael Kelley <>
#include <linux/clocksource.h>
#include <linux/math64.h>
#include <asm/mshyperv.h>
#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
/* Routines called by the VMbus driver */
extern int hv_stimer_alloc(void);
extern void hv_stimer_free(void);
extern int hv_stimer_cleanup(unsigned int cpu);
extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
extern void hv_stimer_legacy_cleanup(unsigned int cpu);
extern void hv_stimer_global_cleanup(void);
extern void hv_stimer0_isr(void);
extern u64 (*hv_read_reference_counter)(void);
extern void hv_init_clocksource(void);
extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
static inline notrace u64
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
u64 scale, offset;
u32 sequence;
* The protocol for reading Hyper-V TSC page is specified in Hypervisor
* Top-Level Functional Specification ver. 3.0 and above. To get the
* reference time we must do the following:
* - READ ReferenceTscSequence
* A special '0' value indicates the time source is unreliable and we
* need to use something else. The currently published specification
* versions (up to 4.0b) contain a mistake and wrongly claim '-1'
* instead of '0' as the special value, see commit c35b82ef0294.
* - ReferenceTime =
* ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
* - READ ReferenceTscSequence again. In case its value has changed
* since our first reading we need to discard ReferenceTime and repeat
* the whole sequence as the hypervisor was updating the page in
* between.
do {
sequence = READ_ONCE(tsc_pg->tsc_sequence);
if (!sequence)
return U64_MAX;
* Make sure we read sequence before we read other values from
* TSC page.
scale = READ_ONCE(tsc_pg->tsc_scale);
offset = READ_ONCE(tsc_pg->tsc_offset);
*cur_tsc = hv_get_raw_timer();
* Make sure we read sequence after we read all other values
* from TSC page.
} while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
static inline notrace u64
hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
u64 cur_tsc;
return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
return NULL;
static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
u64 *cur_tsc)
return U64_MAX;