Messages in this thread | | | Date | Fri, 21 Mar 2008 12:59:48 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [patch 00/13] x86: PAT support updated - v3 |
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Venki Pallipadi wrote: > On Fri, Mar 21, 2008 at 06:29:48AM -0700, H. Peter Anvin wrote: >> venkatesh.pallipadi@intel.com wrote: >>> * UC_MINUS in PAT to provide backward compatibility to /dem/mem mmap users. >> I have to say I think this looks like a good patchset. However, I'd >> like a bit more clarification with regards to the above point? >> > > X seems to use (in that order) > - mmap the range through /dev/mem > - Set MTRR for the range to WC > > I see this happening on one of my test systems with relatively new xorg. > > In this case, when mmap does the reserve for this range, if we give UC mapping > then we will effectively negate the MTRR WC setting with the range being mapped > UC. To accomodate this special use case, we give /dev/mem mmap (only when there > are no other already existing mappings) a UC_MINUS attribute. With that, > if and when X sets MTRR the range will become WC and until that time it will be > UC. We ensure that all page table mappings use UC_MINUS for that range. > > Long term, we want X to switch to /proc/ of /sys interfaces. But, we can also > provide backward compatibility for existing X usage like above. >
Makes total sense. Eventually I think we want to do /proc/mtrr emulation, but for now, this is probably the best option.
-hpa
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