Re: [PATCH] iommu/io-pgtable-arm: Add support for contiguous hint bit

[Daniel Mentz]

On Fri, Jul 3, 2026 at 9:18 AM Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
>
> On Thu, Jun 18, 2026 at 02:32:09PM +0530, Vijayanand Jitta wrote:
> > From: Prakash Gupta <prakash.gupta@xxxxxxxxxxxxxxxx>
> > Add support for the contiguous hint (CONT) bit in ARM LPAE page tables.

[...]

> > Support is gated behind CONFIG_IOMMU_IO_PGTABLE_CONTIG_HINT, which
> > provides a compile-time opt-out for hardware affected by SMMU errata
> > related to the contiguous bit.
>
> I reviewed the errata and didn't find any related to contig that
> required disabling contig, the driver was OK with the ones I
> found.. Did you find something specific?

Arm MMU-700 is affected by erratum 3777127 ("Under invalidation in TBU
possible when using contiguous page table entries"). However, if we
disallow partial unmaps of groups of adjacent translation table
entries, we implicitly apply the workaround ("Ensure that contiguous
page tables are removed using a single range invalidation. Arm
recommends using range invalidations to remove contiguous entries
anyway for performance reasons.")