linux-kernel - Re: [patch 1/3] x86_64: CPA, fix cache attribute inconsistency bug, v2.6.22 backport

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Message-ID: <20080220204422.GE7415@redhat.com>
Date:	Wed, 20 Feb 2008 15:44:22 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	mingo@...e.hu
Cc:	stable@...nel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [patch 1/3] x86_64: CPA, fix cache attribute inconsistency
	bug, v2.6.22 backport

On Wed, Feb 20, 2008 at 03:30:18PM -0500, Vivek Goyal wrote:
> On Fri, Feb 15, 2008 at 08:58:22PM +0100, Ingo Molnar wrote:
> > 
> > fix CPA cache attribute bug in v2.6.23. When phys_base is nonzero
> > (when CONFIG_RELOCATABLE=y) then change_page_attr_addr() miscalculates
> > the secondary alias address by -14 MB (depending on the configured
> > offset).
> > 
> > The default 64-bit kernels of Fedora and Ubuntu are affected:
> > 
> >    $ grep RELOCA /boot/config-2.6.23.9-85.fc8
> >      CONFIG_RELOCATABLE=y
> > 
> >    $ grep RELOC /boot/config-2.6.22-14-generic
> >      CONFIG_RELOCATABLE=y
> > 
> > and probably on many other distros as well.
> > 
> > the bug affects all pages in the first 40 MB of physical RAM that
> > are allocated by some subsystem that does ioremap_nocache() on them:
> > 
> >        if (__pa(address) < KERNEL_TEXT_SIZE) {
> > 
> > Hence we might leave page table entries with inconsistent cache
> > attributes around (pages mapped at both UnCacheable and Write-Back),
> > and we can also set the wrong kernel text pages to UnCacheable.
> > 
> > the effects of this bug can be random slowdowns and other misbehavior.
> > If for example AGP allocates its aperture pages into the first 40 MB
> > of physical RAM, then the -14 MB bug might mark random kernel texto
> > pages as uncacheable, slowing down a random portion of the 64-bit
> > kernel until the AGP driver is unloaded.
> > 
> > Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > Acked-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  arch/x86_64/mm/pageattr.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Index: linux-tmp/arch/x86_64/mm/pageattr.c
> > ===================================================================
> > --- linux-tmp.orig/arch/x86_64/mm/pageattr.c
> > +++ linux-tmp/arch/x86_64/mm/pageattr.c
> > @@ -204,7 +204,7 @@ int change_page_attr_addr(unsigned long 
> >  		if (__pa(address) < KERNEL_TEXT_SIZE) {
> 
> Hi Ingo,
> 
> Should we change above condition also to something like following.
> 
> kernel_phys_start = __pa(__START_KERNEL_map) + phys_base


Oops. Just noticed that __pa() is already taking care of adding phys_base.
So it should probably be.

kernel_phys_start = __pa(__START_KERNEL_map);
kernel_phys_end = kernel_phys_start + KERNEL_TEXT_SIZE;

if (__pa(address) >= kernel_phys_start
	&& __pa(address) <= kernel_phys_end)  

Thanks
Vivek
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