Re: [PATCH v1 0/3] xen/arm: Add option to optionally disable trapping on unmapped mmio

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Tue, May 27, 2025 at 09:03:11PM +0100, Andrew Cooper wrote:
> On 27/05/2025 8:56 pm, Edgar E. Iglesias wrote:
> > From: "Edgar E. Iglesias" <edgar.iglesias@amd.com>
> >
> > This follows up on the virtio-pci discussion and adds a per-domain
> > option to select the behaviour of accesses to unmapped mmio ranges.
> > The new option is trap-unmapped-mmio. For dom0less I negated it to
> > be able to use a boolean prop and keep existing behaviour, i.e
> > trap-unmapped-mmio-disabled.
> >
> > I'm happy with any name though so if you have better ideas please
> > suggest them!
> >
> > For the domain config i followed the example of x86 flags
> > and XEN_X86_MSR_RELXED, creating a flags field for ARM.
> >
> > Thanks,
> > Edgar
> 
> I think this should be common, rather than ARM specific.
> 
> Traditionally on x86, access to unimplemented address space was ignored
> (write discard, read ~0), but these days you do get a machine check on
> certain ranges, which is for all intents and purposes the same as a data
> abort.
> 
> So even if x86 requires it to be false in the short term, I think the
> control ought to be common, so x86 and others can opt in at a later point.

We can do that, we'd need to have different default values though since
x86 wants default false and ARM default true.

> 
> I don't have a good suggestion for the name, but it's not really about
> MMIO space; it's about address space generally.

What about trap-unmapped-access ?

Cheers,
Edgar