Re: [PATCH v1 4/9] iommufd/iova_bitmap: Handle recording beyond the mapped pages

[Avihai Horon <avihaih@nvidia.com>]

On 02/02/2024 15:34, Joao Martins wrote:
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>
> IOVA bitmap is a zerocopy scheme of recording dirty bits that iterate the
> different bitmap user pages at chunks of maximum of PAGE_SIZE/sizeof(struct
> page*) pages.
>
> When the iterations are split up into 64G, the end of the range may be
> broken up in a way that's aligned with a non base page PTE size. This leads
> to only part of the huge page being recorded in the bitmap. Note that in
> pratice this is only a problem for IOMMU dirty tracking i.e. when the
> backing PTEs are in IOMMU hugepages and the bitmap is in base page
> granularity. So far this not something that affects VF dirty trackers
> (which reports and records at the same granularity).
>
> To fix that, if there is a remainder of bits left to set in which the
> current IOVA bitmap doesn't cover, make a copy of the bitmap structure and
> iterate-and-set the rest of the bits remaining. Finally, when advancing the
> iterator, skip all the bits that were set ahead.
>
> Reported-by: Avihai Horon <avihaih@nvidia.com>
> Fixes: f35f22cc760e ("iommu/vt-d: Access/Dirty bit support for SS domains")
> Fixes: 421a511a293f ("iommu/amd: Access/Dirty bit support in IOPTEs")
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Tested-by: Avihai Horon <avihaih@nvidia.com>