linux-kernel - Re: [PATCH v2 1/5] iommu/vt-d: Separate page request queue from SVM

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Message-ID: <a5e0ff3c-a48f-4f2f-bf6a-551ebec21559@linux.intel.com>
Date: Wed, 18 Sep 2024 10:52:12 +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>,
 "j.granados@...sung.com" <j.granados@...sung.com>,
 David Woodhouse <dwmw2@...radead.org>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Klaus Jensen <its@...elevant.dk>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Subject: Re: [PATCH v2 1/5] iommu/vt-d: Separate page request queue from SVM

On 9/15/24 9:49 PM, Jason Gunthorpe wrote:
> On Sat, Sep 14, 2024 at 01:49:44PM +0800, Baolu Lu wrote:
>> On 2024/9/14 10:53, Tian, Kevin wrote:
>>>> From: Baolu Lu<baolu.lu@...ux.intel.com>
>>>> Sent: Saturday, September 14, 2024 9:18 AM
>>>>
>>>> On 9/14/24 8:52 AM, Tian, Kevin wrote:
>>>>>> From: Joel Granados via B4 Relay
>>>>>> <devnull+j.granados.samsung.com@...nel.org>
>>>>>>
>>>>>> From: Joel Granados<j.granados@...sung.com>
>>>>>>
>>>>>> IO page faults are no longer dependent on CONFIG_INTEL_IOMMU_SVM.
>>>>>> Move
>>>>>> all Page Request Queue (PRQ) functions that handle prq events to a new
>>>>>> file in drivers/iommu/intel/prq.c. The page_req_des struct is now
>>>>>> declared in drivers/iommu/intel/prq.c.
>>>>>>
>>>>>> No functional changes are intended. This is a preparation patch to
>>>>>> enable the use of IO page faults outside the SVM/PASID use cases.
>>>>> Do we want to guard it under a new config option e.g.
>>>>> CONFIG_INTEL_IOMMU_IOPF? it's unnecessary to allocate resources
>>>>> for the majority usages which don't require IOPF.
>>>>>
>>>>> Baolu?
>>>> The OS builder doesn't know if Linux will run on a platform with PRI-
>>>> capable devices. They'll probably always enable this option if we
>>>> provide it.
>>> hmm then why do we need a SVM option? In reality I haven't seen
>>> a platform which supports IOPF but no pasid/SVM. so the reason
>>> for whether to have an option should be same between IOPF/SVM.
>>>
>>> IMHO the point of options is to allow reducing footprint of the kernel
>>> image and many options are probably always enabled in distributions...
>> To be honest, I would hope to remove the SVM option some day. It's
>> nothing special except listening to an external notification and
>> synchronize the caches when the page table is updated. It's common to
>> all cases where a page table is shared between the IOMMU and another
>> component.
>>
>> As for CONFIG_INTEL_IOMMU_IOPF, my suggestion is that we don't need to
>> add any unnecessary options unless we see a real need.
> You could possibly bundle the SVA and IOPF options together
> 
> I called the new option on the ARM side CONFIG_ARM_SMMU_V3_IOMMUFD
> which seems like a reasonable cut point against embedded vs server.

Probably I will consider this after this series. This is not intel iommu
specific, hence it's better to make it consistent for all drivers.

Thanks,
baolu