[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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