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

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxx>
> >>
> >> From: Joel Granados<j.granados@xxxxxxxxxxx>
> >>
> >> 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.
>