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From: Alex Williamson <alex.williamson@redhat.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, peterx@redhat.com
Subject: Re: [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping_range()
Date: Fri, 6 Aug 2021 14:17:45 -0600	[thread overview]
Message-ID: <20210806141745.1d8c3e0a.alex.williamson@redhat.com> (raw)
In-Reply-To: <20210806010418.GF1672295@nvidia.com>

On Thu, 5 Aug 2021 22:04:18 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Thu, Aug 05, 2021 at 11:07:35AM -0600, Alex Williamson wrote:
> > @@ -2281,15 +2143,13 @@ static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data)
> >  
> >  	vdev = container_of(device, struct vfio_pci_device, vdev);
> >  
> > -	/*
> > -	 * Locking multiple devices is prone to deadlock, runaway and
> > -	 * unwind if we hit contention.
> > -	 */
> > -	if (!vfio_pci_zap_and_vma_lock(vdev, true)) {
> > +	if (!down_write_trylock(&vdev->memory_lock)) {
> >  		vfio_device_put(device);
> >  		return -EBUSY;
> >  	}  
> 
> Now that this is simplified so much, I wonder if we can drop the
> memory_lock and just use the dev_set->lock?
> 
> That avoids the whole down_write_trylock thing and makes it much more
> understandable?

Hmm, that would make this case a lot easier, but using a mutex,
potentially shared across multiple devices, taken on every non-mmap
read/write doesn't really feel like a good trade-off when we're
currently using a per device rwsem to retain concurrency here.  Thanks,

Alex


  reply	other threads:[~2021-08-06 20:17 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05 17:06 [PATCH 0/7] vfio: device fd address space and vfio-pci mmap invalidation cleanup Alex Williamson
2021-08-05 17:07 ` [PATCH 1/7] vfio: Create vfio_fs_type with inode per device Alex Williamson
2021-08-10  8:43   ` Christoph Hellwig
2021-08-10 14:52     ` Alex Williamson
2021-08-10 14:57       ` Christoph Hellwig
2021-08-10 18:49         ` Peter Xu
2021-08-10 21:16           ` Alex Williamson
2021-08-10 22:18             ` Peter Xu
2021-08-05 17:07 ` [PATCH 2/7] vfio: Export unmap_mapping_range() wrapper Alex Williamson
2021-08-10  8:45   ` Christoph Hellwig
2021-08-10 18:56   ` Peter Xu
2021-08-05 17:07 ` [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping_range() Alex Williamson
2021-08-06  1:04   ` Jason Gunthorpe
2021-08-06 20:17     ` Alex Williamson [this message]
2021-08-10  8:51       ` Christoph Hellwig
2021-08-10 11:57         ` Jason Gunthorpe
2021-08-10 12:55           ` Christoph Hellwig
2021-08-10 21:50             ` Alex Williamson
2021-08-11 11:57               ` Jason Gunthorpe
2021-08-10  8:53   ` Christoph Hellwig
2021-08-10 19:02     ` Peter Xu
2021-08-10 20:51       ` Alex Williamson
2021-08-10 18:48   ` Peter Xu
2021-08-10 19:59     ` Alex Williamson
2021-08-10 20:20       ` Peter Xu
2021-08-05 17:07 ` [PATCH 4/7] vfio,vfio-pci: Add vma to pfn callback Alex Williamson
2021-08-06  1:01   ` Jason Gunthorpe
2021-08-10  9:00     ` Christoph Hellwig
2021-08-10  9:00   ` Christoph Hellwig
2021-08-05 17:08 ` [PATCH 5/7] mm/interval_tree.c: Export vma interval tree iterators Alex Williamson
2021-08-05 17:08 ` [PATCH 6/7] vfio: Add vfio_device_io_remap_mapping_range() Alex Williamson
2021-08-10  9:04   ` Christoph Hellwig
2021-08-05 17:08 ` [PATCH 7/7] vfio/pci: Remove map-on-fault behavior Alex Williamson
2021-08-10  9:11   ` Christoph Hellwig
2021-08-10 15:04     ` Alex Williamson
2021-08-10 20:54   ` Peter Xu
2021-08-10 21:45     ` Alex Williamson
2021-08-10 22:27       ` Peter Xu

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