tree 2d5916dba1f6a7055e6deffae63e77f7cf7bcf8c
parent 8297886712dafa9bd0f641e27ca5352229d2357e
author Ingo Molnar <mingo@elte.hu> 1203105534 +0100
committer Greg Kroah-Hartman <gregkh@suse.de> 1203984848 -0800

x86_64: CPA, fix cache attribute inconsistency bug

no upstream git id as the code has been rewritten.

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@elte.hu>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>