Re: [PATCH 0/2] iommu: Remove iommu_sva_ops::mm_exit()

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>,
	arnd@arndb.de, "Yu, Fenghua" <fenghua.yu@intel.com>,
	gregkh@linuxfoundation.org, iommu@lists.linux-foundation.org,
	zhangfei.gao@linaro.org, linux-accelerators@lists.ozlabs.org
Subject: Re: [PATCH 0/2] iommu: Remove iommu_sva_ops::mm_exit()
Date: Thu, 9 Apr 2020 09:08:21 -0300	[thread overview]
Message-ID: <20200409120821.GE11886@ziepe.ca> (raw)
In-Reply-To: <20200408164802.155a69e3@jacob-builder>

On Wed, Apr 08, 2020 at 04:48:02PM -0700, Jacob Pan wrote:
> > Yes, this is the proper way, when the DMA is stopped and no use of the
> > PASID remains then you can drop the mmu notifier and release the PASID
> > entirely. If that is linked to the lifetime of the FD then forget
> > completely about the mm_struct lifetime, it doesn't matter..
> > 
> Got everything above, thanks a lot.
> 
> If everything is in order with the FD close. Why do we need to 
> "ask IOMMU drivers to silently abort DMA and Page Requests in the
> meantime." in mm_exit notifier? This will be done orderly in unbind
> anyway.

I thought this is exactly what Jean-Phillippe is removing here, it is
a bad idea for the reasons he explained.

> > > Enforcing unbind upon FD close might be a precarious path, perhaps
> > > that is why we have to deal with out of order situation?  
> > 
> > How so? You just put it in the FD release function :)
> 
> I was thinking some driver may choose to defer unbind in some workqueue
> etc.

Doesn't really change anything, the lifetime of the PASID wouuld be
the lifetime of the notifier and the bind, and DMA can't continue
without the notifier registered.

Jason
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