linux-kernel - Re: [PATCH] Fix resume on x86-32 machines

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Date:   Sun, 10 Dec 2017 23:20:50 +0100
From:   Pavel Machek <pavel@....cz>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] Fix resume on x86-32 machines

On Sun 2017-12-10 13:58:23, Andy Lutomirski wrote:
> > On Dec 10, 2017, at 1:38 PM, Pavel Machek <pavel@....cz> wrote:
> > 
> > 
> > After 4.15-rc2, suspend stopped working on Thinkpad X60. 5b06bbc
> > (unintentionally?) reordered stuff with respect to
> > fix_processor_context() on 32-bit and 64-bit. We undo that change on
> > 32-bit.
> > 
> 
> Can you explain what was wrong with the reordering?  Your patch certainly *looks* incorrect.
> 

No, I can't, sorry.

> I'm guessing that the real issue is that 32-bit needs %fs restored
>  early for TLS.

Maybe. I can test patches...

I don't think it would be good idea to revert
5b06bbcfc2c621da3009da8decb7511500c293ed, but since it introduced
regression in -rc2, I believe we should fix the regression now, and
then we can try to provide cleaner solution.

As Linus noted, the code is quite "interesting".
									Pavel


> 
> > While we are at it, fix a comment.
> > 
> > Signed-off-by: Pavel Machek <pavel@....cz>
> > Fixes: 5b06bbcfc2c621da3009da8decb7511500c293ed
> > 
> > diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> > index 5191de1..af7b613 100644
> > --- a/arch/x86/power/cpu.c
> > +++ b/arch/x86/power/cpu.c
> > @@ -216,8 +216,8 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
> >    write_cr0(ctxt->cr0);
> > 
> >    /*
> > -     * now restore the descriptor tables to their proper values
> > -     * ltr is done i fix_processor_context().
> > +     * Now restore the descriptor tables to their proper values
> > +     * ltr is done in fix_processor_context().
> >     */
> > #ifdef CONFIG_X86_32
> >    load_idt(&ctxt->idt);
> > @@ -235,13 +235,11 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
> >    wrmsrl(MSR_GS_BASE, ctxt->gs_base);
> > #endif
> > 
> > -    fix_processor_context();
> > -
> > +#ifdef CONFIG_X86_32
> >    /*
> > -     * Restore segment registers.  This happens after restoring the GDT
> > -     * and LDT, which happen in fix_processor_context().
> > +     * Restore segment registers.
> >     */
> > -#ifdef CONFIG_X86_32
> > +
> >    loadsegment(es, ctxt->es);
> >    loadsegment(fs, ctxt->fs);
> >    loadsegment(gs, ctxt->gs);
> > @@ -252,8 +250,17 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
> >     */
> >    if (boot_cpu_has(X86_FEATURE_SEP))
> >        enable_sep_cpu();
> > +
> > +    fix_processor_context();
> > #else
> > /* CONFIG_X86_64 */
> > +    /*
> > +     * Restore segment registers.  This happens after restoring the GDT
> > +     * and LDT, which happen in fix_processor_context().
> > +     */
> > +    
> > +    fix_processor_context();
> > +
> >    asm volatile ("movw %0, %%ds" :: "r" (ctxt->ds));
> >    asm volatile ("movw %0, %%es" :: "r" (ctxt->es));
> >    asm volatile ("movw %0, %%fs" :: "r" (ctxt->fs));
> > 

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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