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Re: [PATCH 2/2] xen/x86: address violations of Rule 11.3
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 8 Jul 2025 09:20:51 +0200
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- Cc: victorm.lira@xxxxxxx, Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Federico Serafini <federico.serafini@xxxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 08 Jul 2025 07:21:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Jan
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