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Re: [PATCH v3] iommu/amd-vi: do not zero IOMMU MMIO region
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 6 May 2026 17:53:57 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>
- Delivery-date: Wed, 06 May 2026 16:54:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06/05/2026 5:51 pm, Roger Pau Monne wrote:
> Attempting to memset the whole IOMMU MMIO region to zero is dangerous to
> say the least. We don't know what registers might be there, nor which
what->which
> values might be safe for those registers. On a forthcoming platform doing
> the zeroing of the MMIO region does put the IOMMU in a broken state, which
> is not recoverable by the IOMMU initialization procedure in Xen.
>
> Instead just zero the control register, which mimics the current behavior
> with regards to how the control register is handled, and ensures the IOMU
> setup is done with the unit disabled. This approach will need revisiting
> in order to support Preboot DMA Protection.
>
> Fold map_iommu_mmio_region() into its only caller, as the function body is
> just an ioremap() call after the removal of the memset().
>
> Fixes: 0700c962ac2d ("Add AMD IOMMU support into hypervisor")
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper@xxxxxxxxxx>
Thanks.
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