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Re: [PATCH v3 2/3] arm/mpu: Introduce `v8r_el1_msa` device tree property for domains
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Thu, 9 Apr 2026 07:50:41 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Harry Ramsey <Harry.Ramsey@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 09 Apr 2026 07:51:59 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-index: AQHcx1925wGns5uRCkO+Bld4rDba9bXVTXKAgAEOy4A=
- Thread-topic: [PATCH v3 2/3] arm/mpu: Introduce `v8r_el1_msa` device tree property for domains
Hi Andrew,
> On 8 Apr 2026, at 16:40, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 08/04/2026 2:55 pm, Luca Fancellu wrote:
>> diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
>> index cd563cf70684..23df2f24cb09 100644
>> --- a/xen/include/public/arch-arm.h
>> +++ b/xen/include/public/arch-arm.h
>> @@ -355,6 +355,8 @@ struct xen_arch_domainconfig {
>> uint32_t clock_frequency;
>> /* IN */
>> uint8_t arm_sci_type;
>> + /* IN */
>> + uint8_t v8r_el1_msa;
>> };
>> #endif /* __XEN__ || __XEN_TOOLS__ */
>>
>
> This isn't ok as the singular change to the public headers. (Also, I
> haven't had time to fix the other API abuses that have crept into ARM's
> arch domain config)
>
> You're introducing a new hypercall input parameter (which is fine), but
> has no defines (ones private to xen/arch/arm/include/asm/domain.h are
> not permitted for use in the public API), and for which there is no
> input validation. Userspace can currently pass any arbitrary byte here
> which will be copied into d->arch.v8r_el1_msa, not that there's any
> consumer of this field I can see in the series.
>
> Frankly, I think this series is chopped up too much. You really must
> not be introducing new hypercall parameters like this without the whole
> series which lets you `xl create` such a VM.
Thanks for this feedback, while reworking this patch I was wrongly assuming I
had always
zero from the toolstack as this is not supported atm, while instead it’s not
true for malicious
userspace hypercall callers.
The full branch is available at
https://gitlab.com/xen-project/people/lucafancellu/xen/-/commits/r82_rebased?ref_type=heads,
but it doesn’t support domain creation by the toolstack, only by Dom0less.
For the defines, should I have something in the file
xen/xen/include/public/arch-arm.h like this:
#define XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_PMSA 0
#define XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_VMSA 1
And check the value of config->arch.v8r_el1_msa against them in
arch_sanitise_domain_config?
Cheers,
Luca
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