* Andy Lutomirski <l...@amacapital.net> wrote:
> On Jun 12, 2015 12:59 AM, "Jan Beulich" <jbeul...@suse.com> wrote:
> >
> > >>> On 12.06.15 at 01:23, <toshi.k...@hp.com> 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
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