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Re: [PATCH v4 02/21] IOMMU: simplify unmap-on-error in iommu_map()
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Wed, 27 Apr 2022 13:16:02 +0000
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- Cc: Paul Durrant <paul@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHYWH75zDdGe3+po0S/evA91QmE7q0DwOQA
- Thread-topic: [PATCH v4 02/21] IOMMU: simplify unmap-on-error in iommu_map()
On 25/04/2022 09:32, Jan Beulich wrote:
> As of 68a8aa5d7264 ("iommu: make map and unmap take a page count,
> similar to flush") there's no need anymore to have a loop here.
>
> Suggested-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v3: New.
>
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -308,11 +308,9 @@ int iommu_map(struct domain *d, dfn_t df
> d->domain_id, dfn_x(dfn_add(dfn, i)),
> mfn_x(mfn_add(mfn, i)), rc);
>
> - while ( i-- )
> - /* if statement to satisfy __must_check */
> - if ( iommu_call(hd->platform_ops, unmap_page, d, dfn_add(dfn, i),
> - flush_flags) )
> - continue;
> + /* while statement to satisfy __must_check */
> + while ( iommu_unmap(d, dfn, i, flush_flags) )
> + break;
How can this possibly be correct?
The map_page() calls are made one 4k page at a time, and this while loop
is undoing every iteration, one 4k page at a time.
Without this while loop, any failure after the first page will end up
not being unmapped.
~Andrew
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