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From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Jerome Glisse <jglisse@redhat.com>
CC:     Dan Williams <dan.j.williams@intel.com>,
        Christoph Hellwig <hch@lst.de>,
        Ben Skeggs <bskeggs@redhat.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "nouveau@lists.freedesktop.org" <nouveau@lists.freedesktop.org>,
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        "amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 04/15] mm: remove the pgmap field from struct hmm_vma_walk
Thread-Topic: [PATCH 04/15] mm: remove the pgmap field from struct
 hmm_vma_walk
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Date:   Thu, 15 Aug 2019 20:41:33 +0000
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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 =3D 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 =3D=3D 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.

Jason