linux-kernel - Re: [PATCH v3] x86/hyper-v: Fix hv tsc page based sched

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Message-ID: <Z1P9ipIZjI712RTf@liuwe-devbox-debian-v2>
Date: Sat, 7 Dec 2024 07:47:22 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Naman Jain <namjain@...ux.microsoft.com>
Cc: "K . Y . Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Michael Kelley <mhklinux@...look.com>, linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3] x86/hyper-v: Fix hv tsc page based sched_clock for
 hibernation

On Tue, Sep 17, 2024 at 11:09:17AM +0530, Naman Jain wrote:
> read_hv_sched_clock_tsc() assumes that the Hyper-V clock counter is
> bigger than the variable hv_sched_clock_offset, which is cached during
> early boot, but depending on the timing this assumption may be false
> when a hibernated VM starts again (the clock counter starts from 0
> again) and is resuming back (Note: hv_init_tsc_clocksource() is not
> called during hibernation/resume); consequently,
> read_hv_sched_clock_tsc() may return a negative integer (which is
> interpreted as a huge positive integer since the return type is u64)
> and new kernel messages are prefixed with huge timestamps before
> read_hv_sched_clock_tsc() grows big enough (which typically takes
> several seconds).
> 
> Fix the issue by saving the Hyper-V clock counter just before the
> suspend, and using it to correct the hv_sched_clock_offset in
> resume. This makes hv tsc page based sched_clock continuous and ensures
> that post resume, it starts from where it left off during suspend.
> Override x86_platform.save_sched_clock_state and
> x86_platform.restore_sched_clock_state routines to correct this as soon
> as possible.
> 
> Note: if Invariant TSC is available, the issue doesn't happen because
> 1) we don't register read_hv_sched_clock_tsc() for sched clock:
> See commit e5313f1c5404 ("clocksource/drivers/hyper-v: Rework
> clocksource and sched clock setup");
> 2) the common x86 code adjusts TSC similarly: see
> __restore_processor_state() ->  tsc_verify_tsc_adjust(true) and
> x86_platform.restore_sched_clock_state().
> 
> Cc: stable@...r.kernel.org
> Fixes: 1349401ff1aa ("clocksource/drivers/hyper-v: Suspend/resume Hyper-V clocksource for hibernation")
> Co-developed-by: Dexuan Cui <decui@...rosoft.com>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>

Applied to hyperv-fixes with the subject line fixed up. Thanks.