Re: [PATCH v2 04/10] iommupt: Flush the CPU cache after any writes to the page table

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Sep 22, 2025 at 10:12:15AM +0800, Baolu Lu wrote:
> On 8/27/25 01:26, Jason Gunthorpe wrote:
> > @@ -195,6 +218,10 @@ static void record_dirty(struct pt_state *pts,
> >   				dirty_len);
> >   	if (!(dirty->flags & IOMMU_DIRTY_NO_CLEAR)) {
> > +		/*
> > +		 * No write log required because DMA incoherence and atomic
> > +		 * dirty tracking bits can't work together
> > +		 */
> 
> Could you elaborate a bit on this comment? Is this a hardware or
> software requirement?

dirty tracking relies on some kind of atomic operation coherent
between the IOMMU and CPU. AFAIK this is not possible on any arch
unless the IOMMU is working coherently.

> Are there any software checks or enforcement in
> the subsystem?

I expect the iommu drivers to exclude this combination.

Jason