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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
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10
arch/x86/include/asm/vdso/gettimeofday.h
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@@ -238,10 +238,12 @@ static u64 vread_pvclock(void)
#ifdef CONFIG_HYPERV_TIMER
static u64 vread_hvclock(void)
{
u64 ret = hv_read_tsc_page(&hvclock_page);
if (likely(ret != U64_MAX))
ret &= S64_MAX;
return ret;
u64 tsc, time;
if (hv_read_tsc_page_tsc(&hvclock_page, &tsc, &time))
return time & S64_MAX;
return U64_MAX;
}
#endif