On Jun 12, 2015 12:59 AM, "Jan Beulich" <JBeulich@xxxxxxxx> wrote: > > >>> On 12.06.15 at 01:23, <toshi.kani@xxxxxx> wrote: > > 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. > > But it wouldn't be impossible to simply read the MTRRs upon boot, > store the information, disable MTRRs, and correctly use PAT to > achieve the same effect (i.e. the "blindly maps" part of course > would need fixing). This may crash and burn badly when we call a UEFI function or an SMI happens. I think we should just leave the MTRRs alone. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
