linux-kernel - Re: [PATCH] [v4] x86, suspend: Save/restore extra MSR registers for suspend

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Date:	Thu, 17 Sep 2015 07:30:04 +0200
From:	Pavel Machek <pavel@....cz>
To:	Chen Yu <yu.c.chen@...el.com>
Cc:	rjw@...ysocki.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, bp@...en8.de, rui.zhang@...el.com,
	linux-pm@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v4] x86, suspend: Save/restore extra MSR registers for
 suspend

On Thu 2015-08-27 11:18:27, Chen Yu wrote:
> A bug is reported(https://bugzilla.redhat.com/show_bug.cgi?id=1227208)
> that, after resumed from S3, CPU is running at a low speed.
> After investigation, it is found that, BIOS has modified the value
> of THERM_CONTROL register during S3, and changes it from 0 to 0x10,
> since value of 0x10 means CPU can only get 25% of the Duty Cycle,
> this triggers the problem.
> 
> Here is a simple scenario to reproduce the issue:
> 1.Boot up the system
> 2.Get MSR with address 0x19a, it should be 0
> 3.Put the system into sleep, then wake it up
> 4.Get MSR with address 0x19a, it should be 0(actually it shows 0x10)
> 
> Although this is a BIOS issue, it would be more robust for linux to deal
> with this situation. This patch fixes this issue by introducing a framework
> to save/restore specified MSR registers(THERM_CONTROL in this case)
> for suspend/resume.
> 
> When user encounters a problematic platform and needs to protect the
> MSRs during suspending, he can simply add a quirk entry in
> msr_save_dmi_table, and customizes 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 suspended,
> the MSRs indicated by these IDs will be restored to their original values
> before suspended.
> 
> Since both 64/32-bit kernels are affected, this patch covers 64/32-bit
> common 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.
> 
> Tested-by: Marcin Kaszewski <marcin.kaszewski@...el.com>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>

Acked-by: Pavel Machek <pavel@....cz>

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