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SubjectRe: [PATCH] restore sysenter MSRs at resume
Linus Torvalds writes:
>
> On Wed, 7 May 2003 mikpe@csd.uu.se wrote:
> >
> > The patch below hooks sysenter into the driver model and implements
> > a resume() method which restores the sysenter MSRs.
>
> This is wrong.
>
> For one thing, you screw up SMP seriously, by not enabling sysenter on all
> CPU's, only the boot one.

We don't do apm suspend/resume on SMP, so this is no different from the
current situation. I don't know if acpi does it or not.

> For another, we shouldn't have "device drivers" for the CPU. I certainly
> agree about restoring the sysenter MSR's, but they should be restored by
> the CPU-specific code long _before_ we start initializing devices.
>
> So I think we should just make it part of the CPU initialization (which
> should be in two parts: the low-level asm part for the "core" CPU
> registers, and then the high-level C part for things like the MSR's,
> user-space segment stuff etc).
>
> So why not just add an explicit call to "cpu_resume()" in one of the
> "do_magic_resume()" things, instead of playing games with device trees..

Where would cpu_resume() [and cpu_suspend()] live?
arch/i386/kernel/suspend* belong to SOFTWARE_SUSPEND, but I don't
think that approach is desirable when apm mostly works for UP.

I could probably get away with simply having apm.c invoke the C code
in suspend.c, which does restore the SYSENTER MSRs. suspend.c itself
doesn't seem to depend on the SOFTWARE_SUSPEND machinery, but
suspend_asm.S does.

Does that sound reasonable?

> > The patch has a debug printk() for problematic systems that require
> > the fix. If it says your machine didn't preserve the MSRs, please
> > post a note about this to LKML with your machine model, so we can
> > estimate the scope of the problem.
>
> I really think that it should be done unconditionally - there's no point
> in even _expecting_ the BIOS to restore various random MSR's. I can't
> imagine that many do.

It does the restore unconditionally, the check is just informational.

/Mikael
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