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Iglesias" To: Andrew Cooper Cc: xen-devel@lists.xenproject.org, sstabellini@kernel.org, julien@xen.org, bertrand.marquis@arm.com, michal.orzel@amd.com, Volodymyr_Babchuk@epam.com, edgar.iglesias@amd.com Subject: Re: [PATCH v1 0/3] xen/arm: Add option to optionally disable trapping on unmapped mmio Message-ID: References: <20250527195616.874614-1-edgar.iglesias@gmail.com> <2eac2199-f3e2-4fa8-b6e3-f6cbf999d436@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2eac2199-f3e2-4fa8-b6e3-f6cbf999d436@citrix.com> User-Agent: Mutt/2.2.14+84 (2efcabc4) (2025-03-23) 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" > > > > 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