[Bug 253204] Re: MTRR ioctls don't work as documented
D. Hugh Redelmeier
hugh at mimosa.com
Sun Aug 3 22:04:22 UTC 2008
[I got some help from BenC and mjg59 on freenode's #ubuntu-kernel]
It turns out that the kernel's IOCTL code just bails (returns an all-0
struct) if the MTRR size field is >=4G. There is no room in the size
field of struct mtrr_gentry (defined in /usr/include/asm/mtrr.h).
See case MTRRIOC_GET_ENTRY in arch/x86/kernel/cpu/mtrr/if.c
I think that the struct field should be widened. But that may be an ABI
Otherwise, the IOCTL should return an error. Perhaps EOVERFLOW or
This seems to be a general Linux problem and not specific to Ubuntu.
MTRR ioctls don't work as documented
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