linux-kernel - Re: [PATCH][v7] x86, suspend: Save/restore extra MSR registers for suspend

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Date:	Thu, 26 Nov 2015 10:09:40 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Chen Yu <yu.c.chen@...el.com>
Cc:	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
	rjw@...ysocki.net, pavel@....cz, len.brown@...el.com,
	luto@...nel.org, bp@...e.de, linux@...izon.com,
	marcin.kaszewski@...el.com, linux-pm@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][v7] x86, suspend: Save/restore extra MSR registers for
 suspend


* Chen Yu <yu.c.chen@...el.com> wrote:

> A bug was reported that on certain Broadwell platforms, after resuming from S3,
> the CPU is running at an anomalously low speed.
> 
> It turns out that the BIOS has modified the value of the THERM_CONTROL register
> during S3, and changed it from 0 to 0x10, thus enabled clock modulation(bit4),
> but with undefined CPU Duty Cycle(bit1:3) - which causes the problem.
> 
> Here is a simple scenario to reproduce the issue:
> 
>  1. Boot up the system
>  2. Get MSR 0x19a, it should be 0
>  3. Put the system into sleep, then wake it up
>  4. Get MSR 0x19a, it shows 0x10, while it should be 0
> 
> Although some BIOSen want to change the CPU Duty Cycle during S3, in our case we
> don't want the BIOS to do any modification.
> 
> Fix this issue by introducing a more generic x86 framework to save/restore
> specified MSR registers(THERM_CONTROL in this case) for suspend/resume. This
> allows us to fix similar bugs in a much simpler way in the future.
> 
> When the kernel wants to protect certain MSRs during suspending, we simply add a
> quirk entry in msr_save_dmi_table, and customize the MSR registers inside the
> quirk callback, for example:
> 
>   u32 msr_id_need_to_save[] = {MSR_ID0, MSR_ID1, MSR_ID2...};
> 
> and the quirk mechanism ensures that, once resumed from suspend, the MSRs
> indicated by these IDs will be restored to their original, pre-suspend values.
> 
> Since both 64-bit and 32-bit kernels are affected, this patch covers the common
> 64/32-bit suspend/resume code path. And because the MSRs specified by the user
> might not be available or readable in any situation, we use rdmsrl_safe() to
> safely save these MSRs.
> 
> Reported-and-tested-by: Marcin Kaszewski <marcin.kaszewski@...el.com>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Acked-by: Pavel Machek <pavel@....cz>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
> v7:
>  - Use the improved version of changelog, and
>    modify the patch according to:
>    https://patchwork.kernel.org/patch/7637861/
> ---
>  arch/x86/include/asm/msr.h        | 10 +++++
>  arch/x86/include/asm/suspend_32.h |  1 +
>  arch/x86/include/asm/suspend_64.h |  1 +
>  arch/x86/power/cpu.c              | 94 +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 106 insertions(+)

Ok, this version looks mostly good - I've applied it with some other minor edits 
to field and variable naming. Please double check the end result that you'll see 
in the tip-bot notification email once I've pushed it out after some testing.

Thanks,

	Ingo
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