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

Ingo Molnar
2015-11-26T09:09:40Z

* Chen Yu <yu.c.chen@intel.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@intel.com>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Acked-by: Pavel Machek <pavel@ucw.cz>
> Signed-off-by: Chen Yu <yu.c.chen@intel.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