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Re: [PATCH v2 0/2] iommu/amd-vi: remove zeroing of MMIO region
- To: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 6 May 2026 18:55:19 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>
- Delivery-date: Wed, 06 May 2026 16:55:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, May 06, 2026 at 06:49:47PM +0200, Marek Marczykowski-Górecki wrote:
> On Wed, May 06, 2026 at 03:55:12PM +0200, Roger Pau Monne wrote:
> > Hello,
> >
> > Unconditionally zeroing the whole IOMMU MMIO region is dangerous, at
> > least on an upcoming platform this does put the IOMMU in a broken state
> > that's not recoverable by the init procedure in Xen.
> >
> > Get rid of the zeroing, and instead attempt to disable the IOMMU ahead
> > of enabling it.
>
> Just to mention it here, while this looks like a step in the right
> direction, even better would be to not disable IOMMU at boot, but
> reconfigure it - to preserve uninterrupted protection when boot time DMA
> protection is enabled in firmware. But that's definitely more work...
Yes, we are aware of this. But IMO booting with the IOMMU enabled
will be a new feature, this is strictly a fix that we can "safely"
backport to stable branches to deal with broken hardware.
Thanks, Roger.
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