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

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Message-ID: <e0a1347f-877e-445c-9158-7584ae200bff@linux.intel.com>
Date: Sat, 14 Sep 2024 09:18:27 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "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>,
 Jason Gunthorpe <jgg@...pe.ca>, Klaus Jensen <its@...elevant.dk>
Cc: baolu.lu@...ux.intel.com,
 "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 9/14/24 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.

This option could be useful for embedded systems, but I'm not sure if
any embedded systems have VT-d hardware, which is mainly for high-end
PCs or cloud servers.

So, maybe we could leave it as is for now and add it later if we see a
real use case.

Thanks,
baolu