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

[Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>]

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.
> 

Understood. And I am guessing the permissions overloading option should
be available as well? For example, RW or R only. RMRRs are always mapped with
RW.
Why can be this a platform quirk?

> Jan
> 

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