github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-07-27 01:32:21 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

clocksource/hyperv: Implement read_snapshot() for TSC page clocksource

Browse Source 
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
This commit is contained in:
David Woodhouse 2026-06-04 10:35:16 +01:00 committed by Thomas Gleixner
parent ca1ec8bfac
commit c51100f9e2
1 changed files with 27 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
drivers/clocksource/hyperv_timer.c
View File

@ -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
};