linux-kernel - Re: [PATCH v5 07/10] x86/asm/acpi: Fix asmvalidate warnings for wakeup

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Date:	Wed, 10 Jun 2015 15:19:14 +0200
From:	Pavel Machek <pavel@....cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH v5 07/10] x86/asm/acpi: Fix asmvalidate warnings for
 wakeup_64.S

Hi!

> Fix the following asmvalidate warnings:
> 
>    asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64()+0x15: unsupported jump to outside of function
>    asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64()+0x55: unsupported jump to outside of function
>    asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64(): unsupported fallthrough at end of function
>    asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel()+0x9a: unsupported jump to outside of function
>    asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel()+0x116: unsupported jump to outside of function
>    asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel(): unsupported fallthrough at end of function
>    asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel(): missing FP_SAVE/RESTORE macros
> 
> 1. wakeup_long64() isn't a function that can be called.  It's actually
>    redirected to via a return instruction in the entry code.  It
>    shouldn't be annotated as a callable function.  Change ENDPROC ->
>    PROC accordingly.

But I see -> END.

> 2. do_suspend_lowlevel() is a non-leaf callable function, so
>    save/restore the frame pointer with FP_SAVE/RESTORE.

It does not work with the frame pointer itself. Is FP_SAVE/RESTORE
still neccessary? Will you need FP_RESTORE to wakeup_long64, then?

> 3. Remove the unnecessary jump to .Lresume_point, as it just results in
>    jumping to the next instruction (which is a nop because of the
>    align).  Otherwise asmvalidate gets confused by the jump.

It also results in flushing the pipeline. Ok, I guess this one is unneccessary.

> 4. Change the "jmp restore_processor_state" to a call instruction,
>    because jumping outside the function's boundaries isn't allowed.  Now
>    restore_processor_state() will return back to do_suspend_lowlevel()
>    instead of do_suspend_lowlevel()'s caller.
> 
> 5. Remove superfluous rsp changes.

Did you test the changes?

Do you plan to make similar changes to wakeup_32.S?

> diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
> index 8c35df4..7e442be 100644
> --- a/arch/x86/kernel/acpi/wakeup_64.S
> +++ b/arch/x86/kernel/acpi/wakeup_64.S
> @@ -5,6 +5,7 @@
>  #include <asm/page_types.h>
>  #include <asm/msr.h>
>  #include <asm/asm-offsets.h>
> +#include <asm/func.h>
>  
>  # Copyright 2003 Pavel Machek <pavel@...e.cz>, distribute under GPLv2
>  
> @@ -33,13 +34,13 @@ ENTRY(wakeup_long64)
>  
>  	movq	saved_rip, %rax
>  	jmp	*%rax
> -ENDPROC(wakeup_long64)
> +END(wakeup_long64)
>

This should result in no binary code changes, so that's ok with me...

>  ENTRY(do_suspend_lowlevel)
> -	subq	$8, %rsp
> +	FP_SAVE
>  	xorl	%eax, %eax
>  	call	save_processor_state
>

Are you sure? Stuff like
        movq    $saved_context, %rax
        movq    %rsp, pt_regs_sp(%rax)

follows. And you did not modify wakeup_long64, which now receives
different value in saved_rsp.

> @@ -108,8 +108,9 @@ ENTRY(do_suspend_lowlevel)
>  	movq	pt_regs_r15(%rax), %r15
>  
>  	xorl	%eax, %eax
> -	addq	$8, %rsp
> -	jmp	restore_processor_state
> +	call	restore_processor_state
> +	FP_RESTORE
> +	ret
>  ENDPROC(do_suspend_lowlevel)

Umm. I rather liked the direct jump.

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