Re: [Xen-devel] [PATCH v4 01/15] re-work commit 3e06b989 "IOMMU: make page table population preemptible"...

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Aug 01, 2018 at 02:40:14PM +0100, Paul Durrant wrote:
> ...to simplify the implementation and turn need_iommu back into a boolean.
> 
> As noted in [1] the tri-state nature of need_iommu after commit 3e06b989 is
> confusing, as is the implementation of pre-emption using relmem_list.
> 
> This patch instead uses a simple count of pages already populated stored in
> the x86 variant of struct arch_iommu and skips over that number of pages
> if arch_iommu_populate_page_table() is re-invoked after pre-emption.

Urg, all this is quite ugly. It would be quite better if the need for
an IOMMU was decided before populating the p2m (ie: at domain_create
time by passing an extra XEN_DOMCTL_CDF_iommu or some such), so that
the normal addition of RAM would also populate the IOMMU page tables
if not shared.

> [1] https://lists.xenproject.org/archives/html/xen-devel/2018-07/msg01870.html
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks, Roger.

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