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Re: [PATCH v1 0/3] vpci/msix: separate out common MSI-X code
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Mykyta Poturai <Mykyta_Poturai@xxxxxxxx>
- Date: Wed, 28 Oct 2026 08:43:57 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, Stewart Hildebrand <stewart.hildebrand@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 28 Oct 2026 08:44:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHdZUVvbuj2+I/wmEeMfHolzOWTxrcPwg+AgAFhaACAAAvYAIABdxSA
- Thread-topic: [PATCH v1 0/3] vpci/msix: separate out common MSI-X code
On 10/27/26 12:21 PM, Jan Beulich wrote:
> On 27.10.2026 10:39, Mykyta Poturai wrote:
>> On 10/26/26 2:34 PM, Jan Beulich wrote:
>>> On 26.10.2026 13:27, Mykyta Poturai wrote:
>>>> This is preparatory work to make vPCI MSI-X functional on Arm. Split the
>>>> vPCI MSI-X code so that intercepting the MSI-X table and PBA stays x86
>>>> only,
>>>
>>> This likely is related to peculiarities of Arm's interrupt handling, yet
>>> on the surface I can't see why not intercepting MSI-X table accesses
>>> would be safe. Would it be possible to extend background here a little?
>>
>> On Arm most of the work is done by the ITS, so the only thing the device
>> needs to write to the doorbell register is the EventID. Interrupt
>> translation is fully configured in the ITS; it will reject invalid
>> EventIDs and also has a sideband DeviceID, so misconfigured devices
>> cannot trigger each other's interrupts. Memory-wise everything is gated
>> by the IOMMU, so a wrong doorbell address would not pose any risk either.
>
> And a guest fiddling with the mask bits behind Xen's back isn't a problem
> either?
>
> Jan
No. Masking/unmasking an interrupt the guest has already mapped is just
the guest doing its own configuration. Unmasking an unmapped interrupt
will result in it being discarded by the ITS. So I don't see a problem
here either.
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