Re: [Xen-devel] [PATCH RFC] p2m: p2m_mmio_direct set RW permissions

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Elena Ufimtseva [mailto:elena.ufimtseva@xxxxxxxxxx]
> Sent: Tuesday, January 27, 2015 11:06 PM
> 
> On Tue, Jan 27, 2015 at 06:41:39AM +0000, Tian, Kevin wrote:
> > > From: Elena Ufimtseva [mailto:elena.ufimtseva@xxxxxxxxxx]
> > > Sent: Tuesday, January 27, 2015 1:31 AM
> > >
> > > On Mon, Jan 26, 2015 at 05:06:12PM +0000, Jan Beulich wrote:
> > > > >>> On 26.01.15 at 17:57, <elena.ufimtseva@xxxxxxxxxx> wrote:
> > > > > On Fri, Jan 23, 2015 at 10:50:23AM +0000, Jan Beulich wrote:
> > > > >> >>> On 22.01.15 at 18:34, <elena.ufimtseva@xxxxxxxxxx> wrote:
> > > > >> > (XEN)  00000000d56f0000 - 00000000d5fff000 (reserved)
> > > > >>
> > > > >> So this is where one of the RMRRs sits in (and also where
> > > > >> the faults occur according to the two numbers you sent
> > > > >> earlier, which - as others have already said - is an indication
> > > > >> of the reported RMRRs being incomplete), ...
> > > > >>
> > > > >> > (XEN)  00000000d5fff000 - 00000000d6000000 (usable)
> > > > >> > (XEN)  00000000d7000000 - 00000000df200000 (reserved)
> > > > >>
> > > > >> ... and this is the exact range of the other one. But the usable
> > > > >> entry between them is a sign of the firmware not doing the
> > > > >> best job in assigning resources.
> > > > >>
> > > > >> I don't, btw, think that blindly mapping all the reserved regions
> > > > >> into PVH Dom0's P2M would be (or is, if that's what's happening
> > > > >> today) correct - these regions are named reserved for a
> > > > >> reason. In the case here it's actually RAM, not MMIO, and
> > > > >> Dom0 (as well as Xen) has no business accessing these (for others
> > > > >> this may be different, e.g. the LAPIC and IO-APIC ones below,
> > > > >> but Xen learns/knows of them by means different from looking
> > > > >> at the memory map).
> > > > >
> > > > > I understand this this. At the same time I think pv dom0 does exactly
> > > > > this blind mapping. I also tried to map these regions as read-only and
> > > > > that worked. Can be this an option for these ram regions?
> > > >
> > > > No - they're reserved, so there shouldn't be _any_ access to them.
> > > > The only possible workaround I see as acceptable would be the
> > > > already proposed addition of a command line option allowing to
> > > > specify additional RMRR-like regions.
> >
> > yes the proposal RMRR change would allow an user to specify arbitrary
> > regions which should cover such bogus platform.
> 
> Is dom0 rmrr-like region override option is in rmrr design proposal? I
> saw you briefly mentioned this.
> 

current proposal only covers normal VMs, so the proposed enhancements
are in VM config file. For dom0, looks we have to extend cmdline instead.

Thanks
Kevin

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