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From: Peter Xu <peterx@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	eric.auger@redhat.com, cohuck@redhat.com
Subject: Re: [PATCH] vfio/type1: Limit DMA mappings per container
Date: Tue, 2 Apr 2019 10:41:15 +0800	[thread overview]
Message-ID: <20190402024115.GA11008@xz-x1> (raw)
In-Reply-To: <155414977872.12780.13728555131525362206.stgit@gimli.home>

On Mon, Apr 01, 2019 at 02:16:52PM -0600, Alex Williamson wrote:

[...]

> @@ -1081,8 +1088,14 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  		goto out_unlock;
>  	}
>  
> +	if (!atomic_add_unless(&iommu->dma_avail, -1, 0)) {
> +		ret = -ENOSPC;
> +		goto out_unlock;
> +	}
> +
>  	dma = kzalloc(sizeof(*dma), GFP_KERNEL);
>  	if (!dma) {
> +		atomic_inc(&iommu->dma_avail);

This should be the only special path to revert the change.  Not sure
whether this can be avoided by simply using atomic_read() or even
READ_ONCE() (I feel like we don't need atomic ops with dma_avail
because we've had the mutex but it of course it doesn't hurt...) to
replace atomic_add_unless() above to check against zero then we do
+1/-1 in vfio_[un]link_dma() only.  But AFAICT this patch is correct.

Reviewed-by: Peter Xu <peterx@redhat.com>

Thanks,

-- 
Peter Xu

  reply	other threads:[~2019-04-02  2:41 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-01 20:16 [PATCH] vfio/type1: Limit DMA mappings per container Alex Williamson
2019-04-02  2:41 ` Peter Xu [this message]
2019-04-02  4:34   ` Alex Williamson
2019-04-02  5:18     ` Peter Xu
2019-04-02 14:40       ` Alex Williamson
2019-04-02 14:58 ` Cornelia Huck

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