From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E7B24A4301 for ; Thu, 6 Aug 2026 23:36:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786059419; cv=none; b=pdnkDCNsVRvmkFQ7O/zebkYRELahmVgZkYOcFMWlYZSpHMOsioMO6PyP3pJiqgXPscvkQEd4UkfoBb6HlnBxAQjOxYZk1BqtTJdAPJ4n7tuXbWh4eHiFiCeyXDPsUnVIWssVSf+sT73gCwW4614RK5Xfu74wmVdz4ksFYlbGkZY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786059419; c=relaxed/simple; bh=LJwj0H7ygxbdQNHP5MBvYXv85flCoR1qvNC13d+g8ks=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=HbPqEDMFjZq1Z7XOIZ++rufTNJXZQ5yH/CHXlK90y6LdX5Ba4OaN36wKXA1N3TnWENpLvQSWk3HThklyZ6uChDoFYFqxViWNpwy+TAi2+A+D1DsBz0xuBaR6BnlL2n4R8Cl13McrD1kZIW8YkK/ilFVVMmzO4oAA+v1NXjHo7t4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=Z2wEzc1g; arc=none smtp.client-ip=209.85.215.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Z2wEzc1g" Received: by mail-pg1-f197.google.com with SMTP id 41be03b00d2f7-cb5bdd8450dso1769467a12.0 for ; Thu, 06 Aug 2026 16:36:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786059415; x=1786664215; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:from:to:cc:subject:date:message-id :reply-to:content-type; bh=LVVzZOjwmw/JiJ4qXIbPAPAp0QWxfKUo2q2D7ecTrQM=; b=Z2wEzc1gpTtxPNQfGMbLP7AHA3KE5SQvPd0nI9wIKxp2FmlsLP3kHE35Aym4KSTL6t QtAPcxFeEmy4VECb5XMTjpELzxqBcqPEXo4y/ovf/Tq1jQPvyAs42UQyAmR9zv4zyXa6 +HDkaCBPXxI6+ecVZM6JxsrAhLDyr8xcuPfulnf3WAtVbmGKxXzhuwa7g+4HWqkblU/N f1S5wKffIBs64E5lTjR2exF/g8MSkTdNWrNFpP3rYBdgieze5qXIo6u2NIljI5bkXVQd 0ppnnHVjyV+oJxpJbUagcT9AxseOr835ZqH7oeA8sK6NYbEVI/U1Unb/gKLxd7U+hwAm S7uA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786059415; x=1786664215; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to:content-type; bh=LVVzZOjwmw/JiJ4qXIbPAPAp0QWxfKUo2q2D7ecTrQM=; b=gooLyGDhZ43U7MfJn/+myk2qArvrMzaKltRxeiqynVLuLC2sdFKcn62te6dXVPEyrB U5HaxNih9FLZuNbJmTSifxmoNbQvhBokDji4oj0RCzmE7+xkUqGsGtMF05hVMY46RnEN 5ZCYw3TfthhBeTlbMB4uTFa9XGVpRbuwePGcCSO/uA4JT9mVJzGsLKGmIBB4sHHm1Lqp KB9aBg4ti0obcrjiEd3dTyMDfdt+kxOVfTCdUCFPoVa8HjeOrDtz2WyG8TNQwzt1Ie5J tP45VuXadlj+qynCFPoJFuXrZBngvJ9KYrwf8/GR8FOdVJxfZbWZijF1fji6gsDP0Cnj yiqQ== X-Forwarded-Encrypted: i=1; AHgh+Rp6Qcsn8lfZkfhtZ5qaQP4Kl7SM1KaQfgtu+gyWWdqzzVSkmHnv/FoCEWdO7d0YaPVEiog=@vger.kernel.org X-Gm-Message-State: AOJu0YxllyHIAcV+zzvxvZPrIM5HhtiZlqsbMFpbbiegJq9eXJSfJ1kj NEmbgNDHKS9dK0gxijzXCPAwPduPrMSGRU/HYEGD/P53BkuKMT+3WGY3ckDj3fasoNaG2QCDvMv 17PVNzA== X-Received: from pfcy22.prod.google.com ([2002:a05:6a00:93d6:b0:84b:be30:8d22]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:8019:b0:848:4a48:9f9f with SMTP id d2e1a72fcca58-84f4fee000fmr6402250b3a.34.1786059415266; Thu, 06 Aug 2026 16:36:55 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 6 Aug 2026 16:35:42 -0700 In-Reply-To: <20260806233609.212337-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260806233609.212337-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.679.g6767b8d81c-goog Message-ID: <20260806233609.212337-26-seanjc@google.com> Subject: [PATCH v6 25/51] clocksource: hyper-v: Register sched_clock save/restore iff it's necessary From: Sean Christopherson To: Kiryl Shutsemau , Rick Edgecombe , Sean Christopherson , Paolo Bonzini , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , Thomas Gleixner , John Stultz Cc: Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , Miroslav Lichvar , x86@kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Michael Kelley , Tom Lendacky , Nikunj A Dadhania , David Woodhouse , David Woodhouse , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Register the Hyper-V reference counter (refcounter) callbacks for saving and restoring its PV sched_clock, if and only if the refcounter is actually being used for sched_clock. Currently, Hyper-V overrides the save/restore hooks if the reference TSC available, whereas the Hyper-V refcounter code only overrides sched_clock if the reference TSC is available *and* it's not invariant. The flaw is effectively papered over by invoking the "old" save/restore callbacks as part of save/restore, but that's unnecessary and fragile. To avoid introducing more complexity, and to allow for additional cleanups of the PV sched_clock code, move the save/restore hooks and logic into hyperv_timer.c and simply wire up the hooks when overriding sched_clock itself. Note, while the Hyper-V refcounter code is intended to be architecture neutral, CONFIG_PARAVIRT is firmly x86-only, i.e. adding a small amount of x86 specific code (which will be reduced in future cleanups) doesn't meaningfully pollute generic code. Reviewed-by: Michael Kelley Tested-by: Michael Kelley Acked-by: Wei Liu Signed-off-by: Sean Christopherson --- arch/x86/kernel/cpu/mshyperv.c | 58 ------------------------------ drivers/clocksource/hyperv_timer.c | 50 ++++++++++++++++++++++++++ 2 files changed, 50 insertions(+), 58 deletions(-) diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index 3bca987e05c3..d704496d0409 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -275,63 +275,6 @@ static void hv_guest_crash_shutdown(struct pt_regs *regs) } #endif /* CONFIG_CRASH_DUMP */ -static u64 hv_ref_counter_at_suspend; -static void (*old_save_sched_clock_state)(void); -static void (*old_restore_sched_clock_state)(void); - -/* - * Hyper-V clock counter resets during hibernation. Save and restore clock - * offset during suspend/resume, while also considering the time passed - * before suspend. This is to make sure that sched_clock using hv tsc page - * based clocksource, proceeds from where it left off during suspend and - * it shows correct time for the timestamps of kernel messages after resume. - */ -static void save_hv_clock_tsc_state(void) -{ - hv_ref_counter_at_suspend = hv_read_reference_counter(); -} - -static void restore_hv_clock_tsc_state(void) -{ - /* - * Adjust the offsets used by hv tsc clocksource to - * account for the time spent before hibernation. - * adjusted value = reference counter (time) at suspend - * - reference counter (time) now. - */ - hv_adj_sched_clock_offset(hv_ref_counter_at_suspend - hv_read_reference_counter()); -} - -/* - * Functions to override save_sched_clock_state and restore_sched_clock_state - * functions of x86_platform. The Hyper-V clock counter is reset during - * suspend-resume and the offset used to measure time needs to be - * corrected, post resume. - */ -static void hv_save_sched_clock_state(void) -{ - old_save_sched_clock_state(); - save_hv_clock_tsc_state(); -} - -static void hv_restore_sched_clock_state(void) -{ - restore_hv_clock_tsc_state(); - old_restore_sched_clock_state(); -} - -static void __init x86_setup_ops_for_tsc_pg_clock(void) -{ - if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE)) - return; - - old_save_sched_clock_state = x86_platform.save_sched_clock_state; - x86_platform.save_sched_clock_state = hv_save_sched_clock_state; - - old_restore_sched_clock_state = x86_platform.restore_sched_clock_state; - x86_platform.restore_sched_clock_state = hv_restore_sched_clock_state; -} - #ifdef CONFIG_X86_64 DEFINE_STATIC_CALL(hv_hypercall, hv_std_hypercall); EXPORT_STATIC_CALL_TRAMP_GPL(hv_hypercall); @@ -736,7 +679,6 @@ static void __init ms_hyperv_init_platform(void) /* Register Hyper-V specific clocksource */ hv_init_clocksource(); - x86_setup_ops_for_tsc_pg_clock(); hv_vtl_init_platform(); #endif /* diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index df567795d175..4293173c3a27 100644 --- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c @@ -554,10 +554,60 @@ static __always_inline void hv_setup_sched_clock(void *sched_clock) #elif defined CONFIG_PARAVIRT #include +static u64 hv_ref_counter_at_suspend; +static void (*old_save_sched_clock_state)(void); +static void (*old_restore_sched_clock_state)(void); + +/* + * Hyper-V clock counter resets during hibernation. Save and restore clock + * offset during suspend/resume, while also considering the time passed + * before suspend. This is to make sure that sched_clock using hv tsc page + * based clocksource, proceeds from where it left off during suspend and + * it shows correct time for the timestamps of kernel messages after resume. + */ +static void save_hv_clock_tsc_state(void) +{ + hv_ref_counter_at_suspend = hv_read_reference_counter(); +} + +static void restore_hv_clock_tsc_state(void) +{ + /* + * Adjust the offsets used by hv tsc clocksource to + * account for the time spent before hibernation. + * adjusted value = reference counter (time) at suspend + * - reference counter (time) now. + */ + hv_adj_sched_clock_offset(hv_ref_counter_at_suspend - hv_read_reference_counter()); +} +/* + * Functions to override save_sched_clock_state and restore_sched_clock_state + * functions of x86_platform. The Hyper-V clock counter is reset during + * suspend-resume and the offset used to measure time needs to be + * corrected, post resume. + */ +static void hv_save_sched_clock_state(void) +{ + old_save_sched_clock_state(); + save_hv_clock_tsc_state(); +} + +static void hv_restore_sched_clock_state(void) +{ + restore_hv_clock_tsc_state(); + old_restore_sched_clock_state(); +} + static __always_inline void hv_setup_sched_clock(void *sched_clock) { /* We're on x86/x64 *and* using PV ops */ paravirt_set_sched_clock(sched_clock); + + old_save_sched_clock_state = x86_platform.save_sched_clock_state; + x86_platform.save_sched_clock_state = hv_save_sched_clock_state; + + old_restore_sched_clock_state = x86_platform.restore_sched_clock_state; + x86_platform.restore_sched_clock_state = hv_restore_sched_clock_state; } #else /* !CONFIG_GENERIC_SCHED_CLOCK && !CONFIG_PARAVIRT */ static __always_inline void hv_setup_sched_clock(void *sched_clock) {} -- 2.55.0.679.g6767b8d81c-goog