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Date: Wed, 20 Feb 2008 15:30:18 -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 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 kernel_phys_end = kernel_phys_start + KERNEL_TEXT_SIZE if (__pa(address) >= kernel_phys_start && __pa(address) <= kernel_phys_end) Looks like we are trying to see if a physical page has been mapped by kernel text/data region also then change the caching attributes there too. In case of relocatable kernel, not necessarily first 40MB will be mapped by the kernel text/data region, If boot loader decides to load kernel at a higher address and phys_base is non-zero. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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