Re: [Xen-devel] [V1 PATCH] PVH: avoid call to handle_mmio

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Wed, 04 Jun 2014 08:24:15 +0100
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 04.06.14 at 00:00, <mukesh.rathor@xxxxxxxxxx> wrote:
> > handle_mmio() is currently unsafe for pvh guests. A call to it would
> > result in call to vioapic_range that will crash xen since the
> > vioapic ptr in struct hvm_domain is not initialized for pvh guests.
> > 
> > However, one path exists for such a call. If a pvh guest, dom0 or
> > domU, unintentionally touches non-existing memory, an EPT violation
> > would occur. This would result in unconditional call to
> > hvm_hap_nested_page_fault. In that function, because
> > get_gfn_type_access returns p2m_mmio_dm for non existing mfns by
> > default, handle_mmio() will get called. This would result in xen
> > crash instead of the guest crash. This patch addresses that.
> 
> Yes, we definitely want this until being properly handled, no matter
> that crashing the guest here doesn't seem to be the right thing either
> (normal x86 behavior would be to drop writes and return all ones for
> reads).

How about doing the same we do for HVM which is inject GP. Then handle_mmio
would just return 0 for pvh, and hvm_hap_nested_page_fault would not need
to be modified.

Mukesh


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