On 10/28/25 3:44 PM, Shameer Kolothum wrote:
>
>> -----Original Message-----
>> From: Jason Gunthorpe <[email protected]>
>> Sent: 28 October 2025 14:04
>> To: Eric Auger <[email protected]>
>> Cc: Nicolin Chen <[email protected]>; Shameer Kolothum
>> <[email protected]>; [email protected]; qemu-
>> [email protected]; [email protected]; [email protected];
>> [email protected]; Nathan Chen <[email protected]>; Matt Ochs
>> <[email protected]>; [email protected]; [email protected];
>> [email protected]; [email protected];
>> [email protected]; [email protected]; [email protected];
>> [email protected]
>> Subject: Re: [PATCH v4 22/27] hw/arm/smmuv3-accel: Add support for ATS
>>
>> On Tue, Oct 28, 2025 at 02:51:29PM +0100, Eric Auger wrote:
>>>
>>> On 10/28/25 2:41 PM, Jason Gunthorpe wrote:
>>>> On Tue, Oct 28, 2025 at 02:21:32PM +0100, Eric Auger wrote:
>>>>> On 10/28/25 1:16 PM, Jason Gunthorpe wrote:
>>>>>> On Mon, Oct 27, 2025 at 10:53:10AM -0700, Nicolin Chen wrote:
>>>>>>
>>>>>>> Hmm, that sounds a legit reason, though adding the ATS support to
>>>>>>> the emulated SMMUv3 isn't seemingly a small effort...
>>>>>> What is "emulated ATS" anyhow?
>>>>> I guess it means implementing ATS translation requests and capability to
>>>>> send ATS invalidations. something like:
>>>>>
>>>>>
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.
>> kernel.org%2Fall%2F20250628180226.133285-1-clement.mathieu--
>> drif%40eviden.com%2F&data=05%7C02%7Cskolothumtho%40nvidia.com%
>> 7C9f9c8fc639214f54ca0808de162accab%7C43083d15727340c1b7db39efd
>> 9ccc17a%7C0%7C0%7C638972570246014005%7CUnknown%7CTWFpbGZs
>> b3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIs
>> IkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=YQfzKiIcBbKj
>> kIauHU8ELDk15jclFnFcevMMRf7LHF0%3D&reserved=0
>>>> Why would you even want this? The cover letter didn't explain what the
>>>> point was.
>>> well I am just concerned about exposing ATS support to emulated EPs
>>> while we actually do not support it.
>> Sure, that shouldn't be done. There is ACPI/DT tables indicating if the
>> each device supports ATS and qemu should not be marking the emulated
>> EPs as ATS capable in the first place..
>>
>> However, there is no big work with showing EPs as ATS capable. They
>> don't implement an ATC and there is no concept of "translated address"
>> inside qemu so the only requirement to make it "work" is to just NOP
>> the ATC invalidation SMMU commands for those EPs.
> The only case where an emulated endpoint can appear with SMMUv3
> accel enabled is during a hot-plug scenario.
>
> As mentioned elsewhere in this discussion, that can be handled by propagating
> an error from the pci_device_iommu_address_space() path.
>
> I will take a look at that if this is the main concern regarding ATS.
OK thanks!
Eric
>
> Thanks,
> Shameer
>
