linux-kernel - [PATCH AUTOSEL 4.19] x86/hyperv: Set X86_FEATURE_TSC_KNOWN

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Message-ID: <20240918063708.239096-1-sashal@kernel.org>
Date: Wed, 18 Sep 2024 02:37:07 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Michael Kelley <mhklinux@...look.com>,
	Roman Kisel <romank@...ux.microsoft.com>,
	Wei Liu <wei.liu@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	kys@...rosoft.com,
	haiyangz@...rosoft.com,
	sthemmin@...rosoft.com,
	decui@...rosoft.com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	linux-hyperv@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19] x86/hyperv: Set X86_FEATURE_TSC_KNOWN_FREQ when Hyper-V provides frequency

From: Michael Kelley <mhklinux@...look.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@...look.com>
Reviewed-by: Roman Kisel <romank@...ux.microsoft.com>
Link: https://lore.kernel.org/r/20240606025559.1631-1-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@...nel.org>
Message-ID: <20240606025559.1631-1-mhklinux@...look.com>
Signed-off-by: Sasha Levin <sashal@...nel.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 f8b0fa2dbe37..b43f25b3c99d 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -243,6 +243,7 @@ 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.hints & HV_X64_ENLIGHTENED_VMCS_RECOMMENDED) {
-- 
2.43.0