Re: [PATCH 2/2] xen/x86: address violations of Rule 11.3

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 8 Jul 2025, Jan Beulich wrote:
> On 08.07.2025 00:00, Stefano Stabellini wrote:
> > On Tue, 24 Jun 2025, Jan Beulich wrote:
> >> On 24.06.2025 02:20, victorm.lira@xxxxxxx wrote:
> >>> From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> >>>
> >>> Use {get,put}_unaligned_t to ensure that reads and writes are
> >>> safe to perform even on potentially misaligned pointers.
> >>
> >> Also applicable to the Arm patch: Please can such patches mention the
> >> main subject of the rule, not just the number?
> > 
> > +1
> > 
> > 
> >> Overall I'm unconvinced we really want or need this on x86; I'm curious
> >> what Andrew and Roger think.
> > 
> > To be honest, I had a similar reaction to you, which is why I suggested
> > on Matrix to:
> > 
> > - deviate the rule in its entirety on x86
> > - deviate the rule for all mappings except for devmem mappings on ARM
> > 
> > Leaving aside ARM for a second (this is exactly the kind of very
> > arch-specific behavior that is OK to device differently per
> > architecture), would you be OK with deviating the rule in its entirety on
> > x86?
> > 
> > Or do you prefer to continue with this patch?
> 
> Neither. Imo globally deviating rules needs to be done with care. There
> are, in principle, misaligned accesses in x86 which can be made fault
> (and I think this was mentioned before). We want to know of such risks.
> Hence for a rule like this one more fine grained deviation is on order,
> imo.

What fine grained deviation do you have in mind?