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


  • To: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 27 May 2025 21:03:11 +0100
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  • Cc: sstabellini@xxxxxxxxxx, julien@xxxxxxx, bertrand.marquis@xxxxxxx, michal.orzel@xxxxxxx, Volodymyr_Babchuk@xxxxxxxx, edgar.iglesias@xxxxxxx
  • Delivery-date: Tue, 27 May 2025 20:03:20 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 27/05/2025 8:56 pm, Edgar E. Iglesias wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>
>
> 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.

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

~Andrew



 


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