linux-kernel - Re: [PATCH 1/2] x86-32: Fix crashes with CPU hotplug on AMD machines

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Message-ID: <20100812154756.GD2070@aftab>
Date:	Thu, 12 Aug 2010 17:47:56 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	"Roedel, Joerg" <Joerg.Roedel@....com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>,
	"Seidel, Conny" <Conny.Seidel@....com>,
	"Sarathy, Bhavna" <Bhavna.Sarathy@....com>,
	"greg@...ah.com" <greg@...ah.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86-32: Fix crashes with CPU hotplug on AMD
 machines

From: "H. Peter Anvin" <hpa@...or.com>
Date: Thu, Aug 12, 2010 at 11:34:37AM -0400

> On 08/12/2010 07:41 AM, Joerg Roedel wrote:
> > On Thu, Aug 05, 2010 at 07:14:14AM -0700, H. Peter Anvin wrote:
> >> On 08/05/2010 12:45 AM, Roedel, Joerg wrote:
> >> Correct, again.  It's unclear to me if we can get away with the very
> >> simple 64-bit approach -- in particular, not including all the 1:1
> >> mappings in the kernel -- for all future users, though.
> > 
> > Yeah, We could probably use the same symbol names for the trampoline and
> > the swapper page-table on 32 and 64 bit and merge the code that handles
> > it between the architectures. Shouldn't be too difficult. We cook
> > something up :-)
> > But do you mind to take this patch first? It fixes the occurence of an
> > erratum on AMD hardware, it is a quite simple fix compared to the rework
> > suggested. In fact, I would like to have a simple patch to fix the
> > problem first (and backport it as necessary) and then go the way to
> > rework the current code differences between 32 and 64 bit.
> > 
> 
> Agreed.  I do have a concern about the kernel page tables not being
> synchronized into trampoline_pg_dir (it's only an issue for 32-bit
> !PAE), so at the very least we need to keep an eye out for it...

I've been working on what you suggested and the patch boots on a 32-bit
PAE kernel but keeps rebooting on non-PAE after setting the stack_start
on the AP. I could send it out later for you to look at, if you like -
you should be able to spot what I'm missing :)...

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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