linux-kernel - Re: [PATCH v2 1/2] vfio iommu type1: Fix size argument to vfio_find

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Date:   Tue, 6 Dec 2016 12:34:13 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Kirti Wankhede <kwankhede@...dia.com>
Cc:     <pbonzini@...hat.com>, <kraxel@...hat.com>, <cjia@...dia.com>,
        <qemu-devel@...gnu.org>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] vfio iommu type1: Fix size argument to
 vfio_find_dma() during DMA UNMAP.

On Tue, 6 Dec 2016 23:56:54 +0530
Kirti Wankhede <kwankhede@...dia.com> wrote:

> Passing zero for the size to vfio_find_dma() isn't compatible with
> matching the start address of an existing vfio_dma. Doing so triggers a
> corner case. In vfio_find_dma(), when the start address is equal to
> dma->iova and size is 0, check for the end of search range makes it to
> take wrong side of RB-tree. That fails the search even though the address
> is present in mapped dma ranges. Due to this, in vfio_dma_do_unmap(),
> while checking boundary conditions, size should be set to 1 for verifying
> start address of unmap range.
> vfio_find_dma() is also used to verify last address in unmap range with
> size = 0, but in that case address to be searched is calculated with
> size - 1 and so it works correctly.

I think this last sentence should actually read "start + size - 1", or
at least that makes it more understandable for me.  I'll make that
change and apply these. Thanks,

Alex

> Signed-off-by: Kirti Wankhede <kwankhede@...dia.com>
> Signed-off-by: Neo Jia <cjia@...dia.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index a28fbddb505c..8e9e94ccb2ff 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -826,7 +826,7 @@ again:
>  	 * mappings within the range.
>  	 */
>  	if (iommu->v2) {
> -		dma = vfio_find_dma(iommu, unmap->iova, 0);
> +		dma = vfio_find_dma(iommu, unmap->iova, 1);
>  		if (dma && dma->iova != unmap->iova) {
>  			ret = -EINVAL;
>  			goto unlock;