>>> On 13.06.15 at 01:15, <luto@xxxxxxxxxxxxxx> wrote: > 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. I buy the SMI part, but UEFI runtime calls are being done on page tables we construct and control, so attributes could be kept correct without relying on MTRRs. Jan -- 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
