linux-kernel - Re: [PATCH v2 08/12] iommu: Prepare for separating SVA and IOPF

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Date:   Sun, 13 Aug 2023 19:19:51 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     baolu.lu@...ux.intel.com, "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 08/12] iommu: Prepare for separating SVA and IOPF

On 2023/8/11 21:27, Jason Gunthorpe wrote:
> On Fri, Aug 11, 2023 at 09:53:41AM +0800, Baolu Lu wrote:
>> On 2023/8/11 0:47, Jason Gunthorpe wrote:
>>> On Thu, Aug 10, 2023 at 02:35:40AM +0000, Tian, Kevin wrote:
>>>>> From: Baolu Lu<baolu.lu@...ux.intel.com>
>>>>> Sent: Wednesday, August 9, 2023 6:41 PM
>>>>>
>>>>> On 2023/8/9 8:02, Tian, Kevin wrote:
>>>>>>> From: Jason Gunthorpe<jgg@...pe.ca>
>>>>>>> Sent: Wednesday, August 9, 2023 2:43 AM
>>>>>>>
>>>>>>> On Thu, Aug 03, 2023 at 08:16:47AM +0000, Tian, Kevin wrote:
>>>>>>>
>>>>>>>> Is there plan to introduce further error in the future? otherwise this
>>>>> should
>>>>>>>> be void.
>>>>>>>>
>>>>>>>> btw the work queue is only for sva. If there is no other caller this can be
>>>>>>>> just kept in iommu-sva.c. No need to create a helper.
>>>>>>> I think more than just SVA will need a work queue context to process
>>>>>>> their faults.
>>>>>>>
>>>>>> then this series needs more work. Currently the abstraction doesn't
>>>>>> include workqueue in the common fault reporting layer.
>>>>> Do you mind elaborate a bit here? workqueue is a basic infrastructure in
>>>>> the fault handling framework, but it lets the consumers choose to use
>>>>> it, or not to.
>>>>>
>>>> My understanding of Jason's comment was to make the workqueue the
>>>> default path instead of being opted by the consumer.. that is my 1st
>>>> impression but might be wrong...
>>> Yeah, that is one path. Do we have anyone that uses this that doesn't
>>> want the WQ? (actually who even uses this besides SVA?)
>> I am still confused. When we forward iopf's to user space through the
>> iommufd, we don't need to schedule a WQ, right? Or I misunderstood
>> here?
> Yes, that could be true, iommufd could just queue it from the
> interrupt context and trigger a wakeup.
> 
> But other iommufd modes would want to invoke hmm_range_fault() which
> would need the work queue.

Yes. That's the reason why I added below helper

int iopf_queue_work(struct iopf_group *group, work_func_t func)

in the patch 09/12.

Best regards,
baolu