Re: [PATCH v4 2/3] gup: introduce unpin_user_folio_dirty_locked()

[Jason Gunthorpe]

On Thu, Jun 19, 2025 at 05:05:42PM +0800, lizhe.67@xxxxxxxxxxxxx wrote:

> As I understand it, there seem to be some issues with this
> implementation. How can we obtain the value of dma->has_reserved
> (acquiring it within vfio_pin_pages_remote() might be a good option)

Yes, you record it during vfio_pin_pages operations. If VFIO call
iommu_map on something that went down the non-GUP path then it sets
the flag.

> and ensure that this value remains unchanged from the time of
> assignment until we perform the unpin operation? 

Map/unmap are paired and not allowed to race so that isn't an issue.

> I've searched through the code and it appears that there are
> instances where SetPageReserved() is called outside of the
> initialization phase.  Please correct me if I am wrong.

It should not be relevant here, pages under use by VFIO are not
permitted to change it will break things.

Jason