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

[Jason Gunthorpe]

On Tue, Apr 28, 2026 at 09:13:55PM +0800, fangyu.yu at linux.alibaba.com wrote:
> 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.

Jason