linux-kernel - Re: [PATCH v2 08/12] iommu: Prepare for separating SVA and IOPF

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Message-ID: <ZNY3LuW+FMAhK2xf@ziepe.ca>
Date:   Fri, 11 Aug 2023 10:27:10 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 08/12] iommu: Prepare for separating SVA and IOPF

On Fri, Aug 11, 2023 at 09:53:41AM +0800, Baolu Lu wrote:
> On 2023/8/11 0:47, Jason Gunthorpe wrote:
> > On Thu, Aug 10, 2023 at 02:35:40AM +0000, Tian, Kevin wrote:
> > > > From: Baolu Lu<baolu.lu@...ux.intel.com>
> > > > Sent: Wednesday, August 9, 2023 6:41 PM
> > > > 
> > > > On 2023/8/9 8:02, Tian, Kevin wrote:
> > > > > > From: Jason Gunthorpe<jgg@...pe.ca>
> > > > > > Sent: Wednesday, August 9, 2023 2:43 AM
> > > > > > 
> > > > > > On Thu, Aug 03, 2023 at 08:16:47AM +0000, Tian, Kevin wrote:
> > > > > > 
> > > > > > > Is there plan to introduce further error in the future? otherwise this
> > > > should
> > > > > > > be void.
> > > > > > > 
> > > > > > > btw the work queue is only for sva. If there is no other caller this can be
> > > > > > > just kept in iommu-sva.c. No need to create a helper.
> > > > > > I think more than just SVA will need a work queue context to process
> > > > > > their faults.
> > > > > > 
> > > > > then this series needs more work. Currently the abstraction doesn't
> > > > > include workqueue in the common fault reporting layer.
> > > > Do you mind elaborate a bit here? workqueue is a basic infrastructure in
> > > > the fault handling framework, but it lets the consumers choose to use
> > > > it, or not to.
> > > > 
> > > My understanding of Jason's comment was to make the workqueue the
> > > default path instead of being opted by the consumer.. that is my 1st
> > > impression but might be wrong...
> > Yeah, that is one path. Do we have anyone that uses this that doesn't
> > want the WQ? (actually who even uses this besides SVA?)
> 
> I am still confused. When we forward iopf's to user space through the
> iommufd, we don't need to schedule a WQ, right? Or I misunderstood
> here?

Yes, that could be true, iommufd could just queue it from the
interrupt context and trigger a wakeup.

But other iommufd modes would want to invoke hmm_range_fault() which
would need the work queue.

Jason