[PATCH v6 10/25] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC ioctl

[Baolu Lu]

On 6/16/25 14:47, Nicolin Chen wrote:
> On Mon, Jun 16, 2025 at 02:12:04PM +0800, Baolu Lu wrote:
>> On 6/14/25 15:14, Nicolin Chen wrote:
>>> +	if (!viommu->ops || !viommu->ops->get_hw_queue_size ||
>>> +	    !viommu->ops->hw_queue_init_phys) {
>>> +		rc = -EOPNOTSUPP;
>>> +		goto out_put_viommu;
>>> +	}
> Hmm, here it does abort when !viommu->ops->hw_queue_init_phys ..
> 
>>> +	/*
>>> +	 * FIXME once ops->hw_queue_init is introduced, this should check "if
>>> +	 * ops->hw_queue_init_phys". And "access" should be initialized to NULL.
>>> +	 */
>> I just don't follow here. Up until now, only viommu->ops->
>> hw_queue_init_phys has been added, which means the current code only
>> supports hardware queues that access guest memory using physical
>> addresses. The access object is not needed for the other type of
>> hardware queue that uses guest IOVA.
>>
>> So, why not just abort here if ops->hw_queue_init_phys is not supported
>> by the IOMMU driver?
> .. so, it already does.
> 
>> Leave other logics to the patches that introduce
>> ops->hw_queue_init? I guess that would make this patch more readible.
> The patch is doing in the way to support the hw_queue_init_phys
> case only. It is just adding some extra FIXMEs as the guideline
> for the future patch adding hw_queue_init op.
> 
> I personally don't feel these are confusing. Maybe you can help
> point out what specific wording feels odd here? Maybe "FIXME"s
> should be "TODO"s?

Oh, I probably misunderstood the logic here. For both hw_queue_init and
hw_queue_init_phys, using an access object to pin the pages for hardware
access is necessary, right? My understanding was that pinning pages is
only required for hw_queue_init_phys.

> 
> I could also drop all of these guideline if they are considered
> very unnecessary.
> 
> Thanks
> Nicolin

Thanks,
baolu