linux-kernel - Re: [PATCH] x86: General protection fault after STR (32 bit systems only)

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Date:	Sat, 13 Jun 2015 16:20:05 +0200
From:	Pavel Machek <pavel@....cz>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Brian Gerst <brgerst@...il.com>, Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, X86 ML <x86@...nel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: General protection fault after STR (32 bit systems
 only)

On Sat 2015-06-13 00:45:29, Denys Vlasenko wrote:
> On Fri, Jun 12, 2015 at 5:48 PM, Brian Gerst <brgerst@...il.com> wrote:
> > If you follow the convoluted flow of the calls in this file,
> > ...
> 
> Speaking of which. It is indeed quite bad.
> 
> For one, saved_eip is only ever set to point to ret_point:
> 
> ENTRY(saved_eip)        .long   0
> ...
> 
>         movl    $ret_point, saved_eip
> 
> and it has just a single user, where an indirect jump
> through it is performed:
> 
>         # jump to place where we left off
>         movl    saved_eip, %eax
>         jmp     *%eax
> 
> No comments why it is so.
> 
> All this seems to be equivalent to trivial
> 
>         # jump to place where we left off
>         jmp     ret_point
> 
> Am I missing something?

I don't think so. Its just that slowdown was not bad enough tofix it.

...patch would be welcome, and even better if you could check the issue
on 64-bit kernel, too...
									Pavel

-- 
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