Re: [PATCH 04/15] mm: remove the pgmap field from struct hmm_vma_walk

From: Jason Gunthorpe
Date: Thu Aug 15 2019 - 16:41:39 EST

On Thu, Aug 15, 2019 at 04:33:06PM -0400, Jerome Glisse wrote:

> So nor HMM nor driver should dereference the struct page (i do not
> think any iommu driver would either),

Er, they do technically deref the struct page:

nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
struct hmm_range *range)
struct page *page;
page = hmm_pfn_to_page(range, range->pfns[i]);
if (!nouveau_dmem_page(drm, page)) {

nouveau_dmem_page(struct nouveau_drm *drm, struct page *page)
return is_device_private_page(page) && drm->dmem == page_to_dmem(page)

Which does touch 'page->pgmap'

Is this OK without having a get_dev_pagemap() ?

Noting that the collision-retry scheme doesn't protect anything here
as we can have a concurrent invalidation while doing the above deref.