From: Michael Kelley mhklinux@outlook.com

[ Upstream commit 8fcc514809de41153b43ccbe1a0cdf7f72b78e7e ]

A Linux guest on Hyper-V gets the TSC frequency from a synthetic MSR, if available. In this case, set X86_FEATURE_TSC_KNOWN_FREQ so that Linux doesn't unnecessarily do refined TSC calibration when setting up the TSC clocksource.

With this change, a message such as this is no longer output during boot when the TSC is used as the clocksource:

[ 1.115141] tsc: Refined TSC clocksource calibration: 2918.408 MHz

Furthermore, the guest and host will have exactly the same view of the TSC frequency, which is important for features such as the TSC deadline timer that are emulated by the Hyper-V host.

Signed-off-by: Michael Kelley mhklinux@outlook.com Reviewed-by: Roman Kisel romank@linux.microsoft.com Link: https://lore.kernel.org/r/20240606025559.1631-1-mhklinux@outlook.com Signed-off-by: Wei Liu wei.liu@kernel.org Message-ID: 20240606025559.1631-1-mhklinux@outlook.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/cpu/mshyperv.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index e0fd57a8ba84..c3e38eaf6d2f 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -424,6 +424,7 @@ static void __init ms_hyperv_init_platform(void) ms_hyperv.misc_features & HV_FEATURE_FREQUENCY_MSRS_AVAILABLE) { x86_platform.calibrate_tsc = hv_get_tsc_khz; x86_platform.calibrate_cpu = hv_get_tsc_khz; + setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ); }

if (ms_hyperv.priv_high & HV_ISOLATION) {