forked from mirrors/linux
9397fa2ea3
Currently hv_read_tsc_page_tsc() (ab)uses the (valid) time value of U64_MAX as an error return. This breaks the clean wrap-around of the clock. Modify the function signature to return a boolean state and provide another u64 pointer to store the actual time on success. This obviates the need to steal one time value and restores the full counter width. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Michael Kelley <mikelley@microsoft.com> Tested-by: Michael Kelley <mikelley@microsoft.com> # Hyper-V Link: https://lore.kernel.org/r/20230519102715.775630881@infradead.org
115 lines
3.2 KiB
C
115 lines
3.2 KiB
C
/* 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 <mikelley@microsoft.com>
|
|
*/
|
|
|
|
#ifndef __CLKSOURCE_HYPERV_TIMER_H
|
|
#define __CLKSOURCE_HYPERV_TIMER_H
|
|
|
|
#include <linux/clocksource.h>
|
|
#include <linux/math64.h>
|
|
#include <asm/hyperv-tlfs.h>
|
|
|
|
#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
|
|
#define HV_MIN_DELTA_TICKS 1
|
|
|
|
#ifdef CONFIG_HYPERV_TIMER
|
|
|
|
#include <asm/hyperv_timer.h>
|
|
|
|
/* Routines called by the VMbus driver */
|
|
extern int hv_stimer_alloc(bool have_percpu_irqs);
|
|
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 void hv_init_clocksource(void);
|
|
extern void hv_remap_tsc_clocksource(void);
|
|
|
|
extern unsigned long hv_get_tsc_pfn(void);
|
|
extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
|
|
|
|
static __always_inline bool
|
|
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
|
|
u64 *cur_tsc, u64 *time)
|
|
{
|
|
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 false;
|
|
/*
|
|
* Make sure we read sequence before we read other values from
|
|
* TSC page.
|
|
*/
|
|
smp_rmb();
|
|
|
|
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.
|
|
*/
|
|
smp_rmb();
|
|
|
|
} while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
|
|
|
|
*time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
|
|
return true;
|
|
}
|
|
|
|
#else /* CONFIG_HYPERV_TIMER */
|
|
static inline unsigned long hv_get_tsc_pfn(void)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
|
|
{
|
|
return NULL;
|
|
}
|
|
|
|
static __always_inline bool
|
|
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
|
|
static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
|
|
static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
|
|
static inline void hv_stimer_global_cleanup(void) {}
|
|
static inline void hv_stimer0_isr(void) {}
|
|
|
|
#endif /* CONFIG_HYPERV_TIMER */
|
|
|
|
#endif
|