Re: [Xen-devel] [PATCH v2 1/3] xen/pvh: enable and set default MTRR type

From: Wei Liu
Date: Thu May 10 2018 - 07:52:15 EST

On Wed, May 09, 2018 at 04:11:39PM +0100, Roger Pau Monné wrote:
> On Wed, May 09, 2018 at 12:30:16PM +0100, Roger Pau Monné wrote:
> > On Wed, May 09, 2018 at 11:56:40AM +0100, Andrew Cooper wrote:
> > > On 09/05/18 11:21, Roger Pau Monne wrote:
> > > I'm not sure that setting the default MTRR type is going to be a
> > > clever idea in hindsight when we come to doing PCI Passthrough support.
> >
> > Setting the default type to WB is also set by hvmloader, it's just
> > that hvmloader also sets some of the fixed and variable ranges to UC
> > in order to cover the iomem areas.
> >
> > The expectations when doing pci-passthrough is that the guest will
> > always use paging and PAT in order to set the appropriate cache
> > attributes, or else the guest itself will have to program the UC MTRR
> > ranges, I admit that's not very nice however.
> >
> > What about enabling the default MTRR type and setting it to WB in the
> > toolstack for PVH? IMO doing it Xen itself would be wrong.
> I have the following patch to set the default MTRR type, but I think
> if we go down this road then we will also have to set UC MTRRs for
> MMIO areas, which again seems fine to me.

Can you please document the default type(s) to pvh.markdown once
the issue is resolved?