[RFC PATCH 07/11] iommupt: Don't preset D when RISC-V IOMMU dirty tracking on

[fangyu.yu at linux.alibaba.com]

>> From: Fangyu Yu <fangyu.yu at linux.alibaba.com>
>> 
>> When mapping writable pages, the RISC-V format code currently
>> pre-sets the PTE D bit unconditionally.
>> 
>> If hardware dirty tracking is active (DC.tc.GADE set), the IOMMU
>> sets D autonomously on the first write. Pre-setting D makes every
>> new mapping appear dirty immediately and breaks dirty tracking.
>> 
>> Introduce PT_FEAT_RISCV_DIRTY_TRACKING_ACTIVE and, when set, leave
>> D cleared for new writable mappings so hardware can capture the
>> first write. Keep pre-setting D when dirty tracking is inactive.
>> 
>> Only meaningful for second-stage (iohgatp) page tables.
>
>You shouldn't need anything like this, the D bit is managed by the
>iommufd core appropriately. It *should* start out pre-set as that is
>faster when not tacking. Only once dirty tracking is started does D
>get cleared. User space is supposed to assume that everything is dirty
>prior to its first D clear.
>

Thanks, that makes sense. I will drop PT_FEAT_RISCV_DIRTY_TRACKING_ACTIVE
and rely on the iommufd core to manage D bit.

Fangyu

>Jason