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

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Date:	Fri, 15 Feb 2008 21:41:28 +0100
From:	"Oliver Pinter" <oliver.pntr@...il.com>
To:	"Ingo Molnar" <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

hi Ingo,

thx add to http://repo.or.cz/w/linux-2.6.22.y-op.git testing ;)


On 2/15/08, Ingo Molnar <mingo@...e.hu> 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) {
> unsigned long addr2;
> pgprot_t prot2;
> -	addr2 = __START_KERNEL_map + __pa(address);
> +	addr2 = __START_KERNEL_map + __pa(address) - phys_base;
> /* Make sure the kernel mappings stay executable */
> prot2 = pte_pgprot(pte_mkexec(pfn_pte(0, prot)));
> err = __change_page_attr(addr2, pfn, prot2,
> --
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--
Thanks,
Oliver
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