On Thu, Jun 11, 2015 at 05:23:16PM -0600, Toshi Kani wrote: > On Thu, 2015-06-11 at 13:36 -0700, Luis R. Rodriguez wrote: > : > > Pending RIP MTRR patches > > ==================== > > > > There are a few pending series so I wanted to provide a status update > > on those series. > > > > mtrr: bury MTRR - unexport mtrr_add() and mtrr_del() > > > > This is the nail on the MTRR coffin, it will prevent future direct > > access to MTRR code. This will not be posted until all of the below > > patches are in and merged. A possible next step here might be to > > consider separating PAT code from MTRR code and making PAT a first > > class citizen, enabling distributions to disable MTRR code in the > > future. I thought this was possible but for some reason I recently > > thought that there was one possible issue to make this happen. I > > suppose we won't know unless we try, unless of course someone already > > knows, Toshi? > > There are two usages on MTRRs: > 1) MTRR entries set by firmware > 2) MTRR entries set by OS drivers > > We can obsolete 2), but we have no control over 1). As UEFI firmwares > also set this up, this usage will continue to stay. So, we should not > get rid of the MTRR code that looks up the MTRR entries, while we have > no need to modify them. > > Such MTRR entries provide safe guard to /dev/mem, which allows > privileged user to access a range that may require UC mapping while > the /dev/mem driver blindly maps it with WB. MTRRs converts WB to UC in > such a case. > > UEFI memory table has memory attribute, which describes cache types > supported in physical memory ranges. However, this information gets > lost when it it is converted to e820 table. Is there no way to modify CPU capability bits upon boot and kick UEFI to re-evaluate ? In such UEFI cases what happens for instance when Xen is used which does not support MTRR? Luis -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
