Re: [PATCH 4/4] kvm: bios: switch MTRRs to cover only the PCI range and default to WB

[Sheng Yang <sheng@linux.intel.com>]

On Saturday 27 September 2008 21:55:33 Zwane Mwaikambo wrote:
> On Sat, 27 Sep 2008, Avi Kivity wrote:
> > Yang, Sheng wrote:
> > > I think we should do a little more than just write msr to update mtrr.
> > >
> > > Intel SDM 10.11.8 "MTRR consideration in MP Systems" define the
> > > procedure to modify MTRR msr in MP. Especially, step 4 enter no-fill
> > > cache mode(set CR0.CD bit and clean NW bit), step 12 re-enabled the
> > > caching(clear this two bits).
> > >
> > > We based on these behaviors to detect MTRR update.
> >
> > Why not simply flush the mmu on an mtrr write?
> >
> > (though of course I have no objection to doing what the manual says)
>
> Detecting that condition is fine for operating systems which follow it,
> but some don't, including older Linux kernels :( Flushing on MTRR write,
> although being overzealous would be the most robust.

OK, this trade off is reasonable, I will update the mtrr patch.

Hope we won't got problem in so early stage. :)
--
regards
Yang, Sheng