linux-kernel - RE: [PATCH RFC 08/11] iommu: Handle IO page faults directly

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Date:   Tue, 22 Mar 2022 00:39:23 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>
CC:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC 08/11] iommu: Handle IO page faults directly

> From: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Sent: Monday, March 21, 2022 7:36 PM
> 
> On Sun, Mar 20, 2022 at 02:40:27PM +0800, Lu Baolu wrote:
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index c0966fc9b686..4f90b71c6f6e 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -27,6 +27,8 @@
> >  #include <linux/cc_platform.h>
> >  #include <trace/events/iommu.h>
> >
> > +#include "iommu-sva-lib.h"
> > +
> >  static struct kset *iommu_group_kset;
> >  static DEFINE_IDA(iommu_group_ida);
> >
> > @@ -1177,10 +1179,9 @@ int iommu_report_device_fault(struct device
> *dev, struct iommu_fault_event *evt)
> >  	if (!param || !evt)
> >  		return -EINVAL;
> >
> > -	/* we only report device fault if there is a handler registered */
> >  	mutex_lock(&param->lock);
> >  	fparam = param->fault_param;
> > -	if (!fparam || !fparam->handler) {
> > +	if (!fparam) {
> >  		ret = -EINVAL;
> >  		goto done_unlock;
> >  	}
> > @@ -1198,7 +1199,11 @@ int iommu_report_device_fault(struct device
> *dev, struct iommu_fault_event *evt)
> >  		mutex_unlock(&fparam->lock);
> >  	}
> >
> > -	ret = fparam->handler(&evt->fault, fparam->data);
> > +	if (fparam->handler)
> > +		ret = fparam->handler(&evt->fault, fparam->data);
> > +	else
> > +		ret = iommu_queue_iopf(&evt->fault, fparam->data);
> > +
> 
> I like the change, but we'll need to consolidate this, because now if the
> driver registers a fault handler it disables IOPF. We could instead
> prevent registration if an IOPF param is present. We could also just merge
> fparam->handler but eventually I'd like to make IOPF fall back to the
> fault handler registered by device driver, in case of invalid page faults.
> I have a couple patches for this but am still missing some bits.
> 

Probably we need two different fault reporting interfaces:

  iommu_report_device_fault()
  iommu_report_domain_fault()

iommu driver knows the type of faults and just calls individual API
accordingly. fallback is also managed by iommu driver if necessary.

Thanks
Kevin