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clocksource: hyper-v: Adjust hv_read_tsc_page_tsc() to avoid special casing U64_MAX

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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
This commit is contained in:
Peter Zijlstra 2023-05-19 12:21:07 +02:00
parent 77750f78b0
commit 9397fa2ea3
4 changed files with 29 additions and 28 deletions
Download patch file Download diff file Expand all files Collapse all files

24
include/clocksource/hyperv_timer.h
View file

@ -38,8 +38,9 @@ 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 inline notrace u64
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
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;
@ -63,7 +64,7 @@ hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
do {
sequence = READ_ONCE(tsc_pg->tsc_sequence);
if (!sequence)
return U64_MAX;
return false;
/*
* Make sure we read sequence before we read other values from
* TSC page.
@ -82,15 +83,8 @@ hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
} 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);
*time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
return true;
}
#else /* CONFIG_HYPERV_TIMER */
@ -104,10 +98,10 @@ 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)
static __always_inline bool
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
{
return U64_MAX;
return false;
}
static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }