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Re: [PATCH v2 0/2] iommu/amd-vi: remove zeroing of MMIO region

To: Roger Pau Monne <roger.pau@xxxxxxxxxx>

From: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Date: Wed, 6 May 2026 18:49:47 +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>

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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... -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab

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