Re: [for-4.15][PATCH v2 5/5] xen/iommu: x86: Clear the root page-table before freeing the page-tables

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.02.2021 16:28, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> The new per-domain IOMMU page-table allocator will now free the
> page-tables when domain's resources are relinquished. However, the root
> page-table (i.e. hd->arch.pg_maddr) will not be cleared.
> 
> Xen may access the IOMMU page-tables afterwards at least in the case of
> PV domain:
> 
> (XEN) Xen call trace:
> (XEN)    [<ffff82d04025b4b2>] R iommu.c#addr_to_dma_page_maddr+0x12e/0x1d8
> (XEN)    [<ffff82d04025b695>] F iommu.c#intel_iommu_unmap_page+0x5d/0xf8
> (XEN)    [<ffff82d0402695f3>] F iommu_unmap+0x9c/0x129
> (XEN)    [<ffff82d0402696a6>] F iommu_legacy_unmap+0x26/0x63

So if unmap was (also) short-circuited for dying domains, this
path wouldn't be taken and all would be well even without this
change?

Jan