Re: [PATCH v16 12/13] x86/tsc: Switch to native sched clock

Nikunj A. Dadhania
2025-01-08T10:20:22Z

On 1/8/2025 2:04 PM, Nikunj A. Dadhania wrote:
>
>> If you want to take care only of STSC now, I'd take a patch which is known
>> good and tested properly. And that should happen very soon because the merge
>> window is closing in.
>
> In that case, let me limit this only to STSC for now, i will send updated patch.

From: Nikunj A Dadhania <nikunj@amd.com>
Date: Wed, 8 Jan 2025 14:18:04 +0530
Subject: [PATCH] x86/kvmclock: Prefer TSC as the scheduler clock for Secure
TSC guests

Although the kernel switches over to a stable TSC clocksource instead of
kvmclock, the scheduler still keeps on using kvmclock as the sched clock.
This is due to kvm_sched_clock_init() updating the pv_sched_clock()
unconditionally. Do not override the PV sched clock when Secure TSC is
enabled.

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
---
arch/x86/kernel/kvmclock.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index d8fef3a65a35..82c4743a5e7a 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -324,8 +324,10 @@ void __init kvmclock_init(void)
if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);

- flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
- kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
+ if (!cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC)) {
+ flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
+ kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
+ }

x86_platform.calibrate_tsc = kvm_get_tsc_khz;
x86_platform.calibrate_cpu = kvm_get_tsc_khz;
--
2.34.1