Re: [PATCH v6 05/25] iommu/iopf: Handle mm faults - Jean-Philippe Brucker

From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: devicetree@vger.kernel.org, kevin.tian@intel.com, jgg@ziepe.ca,
	linux-pci@vger.kernel.org, robin.murphy@arm.com,
	fenghua.yu@intel.com, hch@infradead.org, linux-mm@kvack.org,
	iommu@lists.linux-foundation.org, zhangfei.gao@linaro.org,
	catalin.marinas@arm.com, felix.kuehling@amd.com, will@kernel.org,
	christian.koenig@amd.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 05/25] iommu/iopf: Handle mm faults
Date: Mon, 4 May 2020 18:25:41 +0200	[thread overview]
Message-ID: <20200504162541.GG170104@myrica> (raw)
In-Reply-To: <9fc0e4cc-1242-bf96-5328-cc9039dcc9b6@linux.intel.com>

On Sun, May 03, 2020 at 01:54:36PM +0800, Lu Baolu wrote:
> On 2020/4/30 22:34, Jean-Philippe Brucker wrote:
> > When a recoverable page fault is handled by the fault workqueue, find the
> > associated mm and call handle_mm_fault.
> > 
> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > ---
> > v5->v6: select CONFIG_IOMMU_SVA
> > ---
> >   drivers/iommu/Kconfig      |  1 +
> >   drivers/iommu/io-pgfault.c | 79 +++++++++++++++++++++++++++++++++++++-
> >   2 files changed, 78 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > index 4f33e489f0726..1e64ee6592e16 100644
> > --- a/drivers/iommu/Kconfig
> > +++ b/drivers/iommu/Kconfig
> > @@ -109,6 +109,7 @@ config IOMMU_SVA
> >   config IOMMU_PAGE_FAULT
> >   	bool
> > +	select IOMMU_SVA
> 
> It would be better to move this to the previous patch.
> 
[...]
> > @@ -104,6 +156,29 @@ static void iopf_handle_group(struct work_struct *work)
> >    *
> >    * Add a fault to the device workqueue, to be handled by mm.
> >    *
> > + * This module doesn't handle PCI PASID Stop Marker; IOMMU drivers must discard
> > + * them before reporting faults. A PASID Stop Marker (LRW = 0b100) doesn't
> > + * expect a response. It may be generated when disabling a PASID (issuing a
> > + * PASID stop request) by some PCI devices.
> > + *
> > + * The PASID stop request is issued by the device driver before unbind(). Once
> > + * it completes, no page request is generated for this PASID anymore and
> > + * outstanding ones have been pushed to the IOMMU (as per PCIe 4.0r1.0 - 6.20.1
> > + * and 10.4.1.2 - Managing PASID TLP Prefix Usage). Some PCI devices will wait
> > + * for all outstanding page requests to come back with a response before
> > + * completing the PASID stop request. Others do not wait for page responses, and
> > + * instead issue this Stop Marker that tells us when the PASID can be
> > + * reallocated.
> > + *
> > + * It is safe to discard the Stop Marker because it is an optimization.
> > + * a. Page requests, which are posted requests, have been flushed to the IOMMU
> > + *    when the stop request completes.
> > + * b. We flush all fault queues on unbind() before freeing the PASID.
> > + *
> > + * So even though the Stop Marker might be issued by the device *after* the stop
> > + * request completes, outstanding faults will have been dealt with by the time
> > + * we free the PASID.
> > + *
> >    * Return: 0 on success and <0 on error.
> >    */
> >   int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)
> > 
> 
> The same for the comments.

I think I'll squash both patches, probably doesn't make it harder to
review.

Thanks,
Jean

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