diff options
| author | David Woodhouse <dwmw@amazon.co.uk> | 2026-06-04 10:35:16 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@kernel.org> | 2026-06-05 14:25:03 +0200 |
| commit | c51100f9e26857f2b2376d5cd657a15f52b9e05c (patch) | |
| tree | b9630f53aca5f8fb6c3b25c7fb87f3db7380968d | |
| parent | ca1ec8bfac8c95d0fed9e3611ea21400d1f37262 (diff) | |
clocksource/hyperv: Implement read_snapshot() for TSC page clocksource
Implement the read_snapshot() callback for the Hyper-V TSC page clock-
source. This returns the derived 10MHz reference time (for timekeeping)
while also providing the raw TSC value that was used to compute it.
When the TSC page is valid, hv_read_tsc_page_tsc() atomically captures both
values from a single RDTSC inside the sequence-counter protected read. When
the TSC page is invalid (sequence == 0), the hw_csid and hw_cycles are set
to zero indicating no value is available.
This enables ktime_get_snapshot_id() to provide the raw TSC to consumers
like KVM's master clock when running nested guests under Hyper-V.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Assisted-by: Kiro:claude-opus-4.6-1m
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://patch.msgid.link/20260604095755.64849-2-dwmw2@infradead.org
| -rw-r--r-- | drivers/clocksource/hyperv_timer.c | 37 |
1 files changed, 27 insertions, 10 deletions
diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index e9f5034a1bc8..df567795d175 100644 --- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c @@ -444,6 +444,22 @@ static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg) return read_hv_clock_tsc(); } +static u64 notrace read_hv_clock_tsc_cs_snapshot(struct clocksource *arg, + struct clocksource_hw_snapshot *chs) +{ + u64 time; + + if (hv_read_tsc_page_tsc(tsc_page, &chs->hw_cycles, &time)) { + chs->hw_csid = CSID_X86_TSC; + } else { + chs->hw_cycles = 0; + chs->hw_csid = CSID_GENERIC; + time = read_hv_clock_msr(); + } + + return time; +} + static u64 noinstr read_hv_sched_clock_tsc(void) { return (read_hv_clock_tsc() - hv_sched_clock_offset) * @@ -492,18 +508,19 @@ static int hv_cs_enable(struct clocksource *cs) #endif static struct clocksource hyperv_cs_tsc = { - .name = "hyperv_clocksource_tsc_page", - .rating = 500, - .read = read_hv_clock_tsc_cs, - .mask = CLOCKSOURCE_MASK(64), - .flags = CLOCK_SOURCE_IS_CONTINUOUS, - .suspend= suspend_hv_clock_tsc, - .resume = resume_hv_clock_tsc, + .name = "hyperv_clocksource_tsc_page", + .rating = 500, + .read = read_hv_clock_tsc_cs, + .read_snapshot = read_hv_clock_tsc_cs_snapshot, + .mask = CLOCKSOURCE_MASK(64), + .flags = CLOCK_SOURCE_IS_CONTINUOUS, + .suspend = suspend_hv_clock_tsc, + .resume = resume_hv_clock_tsc, #ifdef HAVE_VDSO_CLOCKMODE_HVCLOCK - .enable = hv_cs_enable, - .vdso_clock_mode = VDSO_CLOCKMODE_HVCLOCK, + .enable = hv_cs_enable, + .vdso_clock_mode = VDSO_CLOCKMODE_HVCLOCK, #else - .vdso_clock_mode = VDSO_CLOCKMODE_NONE, + .vdso_clock_mode = VDSO_CLOCKMODE_NONE, #endif }; |