Re: [Xen-devel] [PATCH 5/5] docs/pvh: document initial MTRR state

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, May 14, 2018 at 05:16:10PM +0100, Roger Pau Monné wrote:
> On Mon, May 14, 2018 at 05:03:52PM +0100, Wei Liu wrote:
> > On Thu, May 10, 2018 at 06:15:05PM +0100, Roger Pau Monne wrote:
> > > Provided to both Dom0 and DomUs.
> > > 
> > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > ---
> > > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > > Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> > > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > > Cc: Julien Grall <julien.grall@xxxxxxx>
> > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > > Cc: Tim Deegan <tim@xxxxxxx>
> > > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > ---
> > >  docs/misc/pvh.markdown | 15 +++++++++++++++
> > >  1 file changed, 15 insertions(+)
> > > 
> > > diff --git a/docs/misc/pvh.markdown b/docs/misc/pvh.markdown
> > > index e85fb15374..639401a887 100644
> > > --- a/docs/misc/pvh.markdown
> > > +++ b/docs/misc/pvh.markdown
> > > @@ -92,3 +92,18 @@ event channels. Delivery of those interrupts can be 
> > > configured in the same way
> > >  as HVM guests, check xen/include/public/hvm/params.h and
> > >  xen/include/public/hvm/hvm\_op.h for more information about available 
> > > delivery
> > >  methods.
> > > +
> > > +## MTRR ##
> > > +
> > > +### Unprivileged guests ###
> > > +
> > > +PVH guests are booted with the default MTRR type set to write-back and 
> > > MTRR
> > > +enabled. This allows DomUs to start with a sane MTRR state. Note that 
> > > this will
> > > +have to be revisited when pci-passthrough is added to PVH in order to 
> > > set MMIO
> > > +regions as UC.
> > 
> > My reading is "revisited" implies the default type will change. In fact
> > it shouldn't. We should clarify: for ram it will remain WB, for MMIO
> > holes it will be UC.
> >
> > Please correct me if I'm wrong.
> 
> That's correct. I've used "revisited" here in the sense that Xen might
> change the default type to UC and set the RAM regions as WB using
> variable MTRR ranges for example.
> 
> I simply wanted to remark that the way RAM is set to WB is currently
> done using the default MTRR type. RAM will always be set of WB for PVH
> in MTRR, however the way to achieve it might change.
> 
> What about adding:
> 
> "Xen guarantees that RAM regions will always have the WB cache type
> set in the initial MTRR state, either set by the default MTRR type or
> by other means."
> 

Sounds good to me.

Wei.

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