From 79ccb0693a99e1b91eba95c6bd32a3e02be156ae Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 24 Jan 2026 00:17:55 +0100 Subject: [PATCH] x86/tsc: Handle CLOCK_SOURCE_VALID_FOR_HRES correctly Unconditionally setting the CLOCK_SOURCE_VALID_FOR_HRES for the real TSC clocksource is wrong as there is no guarantee that the early TSC was validated for high resolution mode. Set the flag only when the early TSC was validated as otherwise the clocksource selection might enable high resolution mode with a TSC of unknown quality and possibly no way to back out once it is discovered to be unsuitable. Signed-off-by: Thomas Gleixner Link: https://patch.msgid.link/20260123231521.790598171@kernel.org --- arch/x86/kernel/tsc.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index f31046f98a92..9ccd58c29409 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1200,7 +1200,6 @@ static struct clocksource clocksource_tsc = { .read = read_tsc, .mask = CLOCKSOURCE_MASK(64), .flags = CLOCK_SOURCE_IS_CONTINUOUS | - CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_CAN_INLINE_READ | CLOCK_SOURCE_MUST_VERIFY | CLOCK_SOURCE_VERIFY_PERCPU | @@ -1411,6 +1410,15 @@ static void tsc_refine_calibration_work(struct work_struct *work) have_art = true; clocksource_tsc.base = &art_base_clk; } + + /* + * Transfer the valid for high resolution flag if it was set on the + * early TSC already. That guarantees that there is no intermediate + * clocksource selected once the early TSC is unregistered. + */ + if (clocksource_tsc_early.flags & CLOCK_SOURCE_VALID_FOR_HRES) + clocksource_tsc.flags |= CLOCK_SOURCE_VALID_FOR_HRES; + clocksource_register_khz(&clocksource_tsc, tsc_khz); unreg: clocksource_unregister(&clocksource_tsc_early);