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

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Message-ID: <BN9PR11MB527611131A808B78C8E0E8388C662@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Sat, 14 Sep 2024 02:53:05 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Baolu Lu <baolu.lu@...ux.intel.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: "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

> 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...

> 
> 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.
>