* Andy Lutomirski <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. Not to mention suspend/resume, reboot and other goodies where the firmware might pop up expecting intact MTRRs. Btw., doesn't a lack of MTRRs imply UC? So is 'crash and burn' possible in most cases? Isn't it just 'executes slower than before'? Thanks, Ingo -- 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
