linux-kernel - Re: [PATCH v2 0/5] iommu: Enable user space IOPFs in non-PASID and non-svm cases

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Message-ID: <20240916085054.gpan37ds7ea45pgh@joelS2.panther.com>
Date: Mon, 16 Sep 2024 10:50:54 +0200
From: Joel Granados <j.granados@...sung.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
CC: David Woodhouse <dwmw2@...radead.org>, Lu Baolu
	<baolu.lu@...ux.intel.com>, 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>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, Klaus Jensen
	<k.jensen@...sung.com>
Subject: Re: [PATCH v2 0/5] iommu: Enable user space IOPFs in non-PASID and
 non-svm cases

On Sat, Sep 14, 2024 at 12:48:31AM +0000, Tian, Kevin wrote:
> > From: Joel Granados via B4 Relay
> > <devnull+j.granados.samsung.com@...nel.org>
> > 
> > This series makes use of iommufd_hwpt_replace_device to execute
> > non-pasid/non-svm user space IOPFs. Our main motivation is to enable
> > user-space driver driven device verification without SVM/PASID.
> 
> can you elaborate why IOPFs are necessary to help verify such usage?

In retrospect "enable" might not be the best word to use here. We are not
"enabling" user-space driver driven device verification as it is already
enabled; you could already poke a device from user space. But the whole poke
space was not available, you could not test IOPF without having an SVM/PASID
capable IOMMU. Therefore a better wording would be "Our main motivation is to
expand or facilitate user-space driver driven device verification by enabling
IOPF without SMV/PASID".

Does this address your concern?

> 
> > 
> > What?
> >   * Enable IO page fault handling in user space for a non-pasid, non-svm
> >     and non-virtualised use case.
> >   * Move IOMMU_IOPF configuration from INTEL_IOMMU_SVM into
> > INTEL_IOMMU.
> >   * Move all page request queue related logic to a new (prq.c) file.
> >   * Remove PASID checks from PRQ event handling as well as PRQ
> >     initialization.
> >   * Allow execution of IOMMU_HWPT_ALLOC with a valid fault id
> >     (IOMMU_HWPT_FAULT_ID_VALID)
> >   * Insert a zero handle into the PASID array in dev->iommu_group when
> >     replacing the old HWPT with an IOPF enabled HWPT.
> 
> the last bullet is stale now.
oops. Missed that one; will correct in next version 

> 
> btw a selftest is expected too.
I'll figure this out for the next version.

Thx for the review

Best
-- 

Joel Granados