diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2023-05-19 13:21:07 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-06-05 22:11:07 +0300 |
| commit | 9397fa2ea3e7634f61da1ab76b9eb88ba04dfdfc (patch) | |
| tree | f7e754cc61e0394b21845060b3f41f6b5f7bc450 /drivers/clocksource | |
| parent | 77750f78b0b3247c64b9821b49158cafe0506880 (diff) | |
| download | linux-9397fa2ea3e7634f61da1ab76b9eb88ba04dfdfc.tar.xz | |
clocksource: hyper-v: Adjust hv_read_tsc_page_tsc() to avoid special casing U64_MAX
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
Diffstat (limited to 'drivers/clocksource')
| -rw-r--r-- | drivers/clocksource/hyperv_timer.c | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index bcd9042a0c9f..c643bfe2f3d4 100644 --- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c @@ -393,14 +393,20 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void) } EXPORT_SYMBOL_GPL(hv_get_tsc_page); -static u64 notrace read_hv_clock_tsc(void) +static notrace u64 read_hv_clock_tsc(void) { - u64 current_tick = hv_read_tsc_page(hv_get_tsc_page()); + u64 cur_tsc, time; - if (current_tick == U64_MAX) - current_tick = hv_get_register(HV_REGISTER_TIME_REF_COUNT); + /* + * The Hyper-V Top-Level Function Spec (TLFS), section Timers, + * subsection Refererence Counter, guarantees that the TSC and MSR + * times are in sync and monotonic. Therefore we can fall back + * to the MSR in case the TSC page indicates unavailability. + */ + if (!hv_read_tsc_page_tsc(tsc_page, &cur_tsc, &time)) + time = hv_get_register(HV_REGISTER_TIME_REF_COUNT); - return current_tick; + return time; } static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg) |