Re: [Xen-devel] [RFC 0 PATCH 3/3] PVH dom0: construct_dom0 changes

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Fri, 27 Sep 2013 07:54:39 +0100
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 27.09.13 at 02:17, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> >>> wrote:
> > On Thu, 26 Sep 2013 09:02:41 +0100 "Jan Beulich"
> > <JBeulich@xxxxxxxx> wrote:
> >> >>> On 25.09.13 at 23:03, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> >> >>> wrote:
> >> > +/*
> >> > + * Set the 1:1 map for all non-RAM regions for dom 0. Thus,
> >> > dom0 will have
> >> > + * the entire io region mapped in the EPT/NPT.
> >> > + *
> >> > + * PVH FIXME: The following doesn't map MMIO ranges when they
> >> > sit above the
> >> > + *            highest E820 covered address.
> >> 
> >> This absolutely needs fixing before this can go in.
> > 
> > Any suggestions on how to fix it? Mapping all the way to end could
> > result in a huge hap table. 
> 
> You'll probably need a call down from Dom0 telling you where it
> finds/puts MMIO resources. Or perhaps that could be mapped
> in on demand from the EPT fault handler (since these regions
> shouldn't be subject to DMA, and hence IOMMU faults shouldn't
> occur - perhaps that's even a reason to not share page tables
> at least in dom0-strict mode)?

Thinking about mapping in on demand from the EPT fault handler, how
would I know if the access beyond last e820 entry is genuine and not 
a faulty pte in a buggy guest? Could I consult the mmconfig table (?) 
or the ACPI table in xen? Any pointers would be helpful... my 
knowledge runs out quickly here.

FWIW, at present pv-ops linux doesn't allow any mmio access beyond
the last e820 entry. So, we'd need a fix there too. In my very orig
patch, I was updating all IO mappings on demand by putting hook
in linux native_pte_update if it was _PAGE_BIT_IOMAP. Another 
possibility would be do that for any mappings above the last
e820 entry. What do you think?

For testing purposes, do you have reference for hardware? I don't see 
any here with such configuration.

thanks
mukesh

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