[PATCH v5] iommu/io-pgtable-arm: Add support for contiguous hint bit

[Vijayanand Jitta]

On 9/25/2026 4:25 AM, Jason Gunthorpe wrote:
> On Thu, Sep 24, 2026 at 01:36:12PM -0700, Daniel Mentz wrote:
> 
>> Interaction with Hardware Dirty Tracking (IO_PGTABLE_QUIRK_ARM_HD)
>>
>> When Hardware Dirty Tracking (ARM_LPAE_PTE_DBM) is enabled on Stage-1 tables:
>>  * In visit_dirty() / arm_lpae_read_and_clear_dirty(), dirty bits are
>> queried and cleared on a page-by-page granularity
>> (iopte_set_writeable_clean(ptep)).
>>  * If a single 4KB page within a 64KB CONT group is marked clean while
>> neighboring pages remain marked dirty/writeable, the descriptors in
>> that group will differ in access permissions (AP[2]).
>>  * According to Arm ARM D8.3.1, all descriptors in a contiguous block
>> must share identical permissions and attributes. If dirty tracking is
>> active on a domain, consider whether IO_PGTABLE_QUIRK_ARM_NO_CONT_HINT
>> should be set or whether CONT sizes should be suppressed when
>> IO_PGTABLE_QUIRK_ARM_HD is active.
> 
> This is right, handling dirty and CONT together is a PITA. You should
> probably make them exclusive for this simplified implementation.
> 
> SMMUv3 is the only user of dirty and it will switch to iommupt which
> does all this right.
> 
> Jason

Sure, I'll set IO_PGTABLE_QUIRK_ARM_NO_CONT_HINT when IO_PGTABLE_QUIRK_ARM_HD is supported.