On 2026-01-15 at 17:18 +1100, Matthew Brost <[email protected]> wrote... > On Wed, Jan 14, 2026 at 09:57:31PM -0800, Matthew Brost wrote: > > On Thu, Jan 15, 2026 at 04:27:26PM +1100, Alistair Popple wrote: > > > On 2026-01-15 at 06:19 +1100, Francois Dugast <[email protected]> > > > wrote... > > > > From: Matthew Brost <[email protected]> > > > > > > > > Reinitialize metadata for large zone device private folios in > > > > zone_device_page_init prior to creating a higher-order zone device > > > > private folio. This step is necessary when the folio’s order changes > > > > dynamically between zone_device_page_init calls to avoid building a > > > > corrupt folio. As part of the metadata reinitialization, the dev_pagemap > > > > must be passed in from the caller because the pgmap stored in the folio > > > > page may have been overwritten with a compound head. > > > > > > Thanks for fixing, a couple of minor comments below. > > > > > > > Cc: Zi Yan <[email protected]> > > > > Cc: Alistair Popple <[email protected]> > > > > Cc: adhavan Srinivasan <[email protected]> > > > > Cc: Nicholas Piggin <[email protected]> > > > > Cc: Michael Ellerman <[email protected]> > > > > Cc: "Christophe Leroy (CS GROUP)" <[email protected]> > > > > Cc: Felix Kuehling <[email protected]> > > > > Cc: Alex Deucher <[email protected]> > > > > Cc: "Christian König" <[email protected]> > > > > Cc: David Airlie <[email protected]> > > > > Cc: Simona Vetter <[email protected]> > > > > Cc: Maarten Lankhorst <[email protected]> > > > > Cc: Maxime Ripard <[email protected]> > > > > Cc: Thomas Zimmermann <[email protected]> > > > > Cc: Lyude Paul <[email protected]> > > > > Cc: Danilo Krummrich <[email protected]> > > > > Cc: David Hildenbrand <[email protected]> > > > > Cc: Oscar Salvador <[email protected]> > > > > Cc: Andrew Morton <[email protected]> > > > > Cc: Jason Gunthorpe <[email protected]> > > > > Cc: Leon Romanovsky <[email protected]> > > > > Cc: Lorenzo Stoakes <[email protected]> > > > > Cc: Liam R. Howlett <[email protected]> > > > > Cc: Vlastimil Babka <[email protected]> > > > > Cc: Mike Rapoport <[email protected]> > > > > Cc: Suren Baghdasaryan <[email protected]> > > > > Cc: Michal Hocko <[email protected]> > > > > Cc: Balbir Singh <[email protected]> > > > > Cc: [email protected] > > > > Cc: [email protected] > > > > Cc: [email protected] > > > > Cc: [email protected] > > > > Cc: [email protected] > > > > Cc: [email protected] > > > > Cc: [email protected] > > > > Cc: [email protected] > > > > Fixes: d245f9b4ab80 ("mm/zone_device: support large zone device private > > > > folios") > > > > Signed-off-by: Matthew Brost <[email protected]> > > > > Signed-off-by: Francois Dugast <[email protected]> > > > > --- > > > > arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- > > > > drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 2 +- > > > > drivers/gpu/drm/drm_pagemap.c | 2 +- > > > > drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- > > > > include/linux/memremap.h | 9 ++++++--- > > > > lib/test_hmm.c | 4 +++- > > > > mm/memremap.c | 20 +++++++++++++++++++- > > > > 7 files changed, 32 insertions(+), 9 deletions(-) > > > > > > > > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c > > > > b/arch/powerpc/kvm/book3s_hv_uvmem.c > > > > index e5000bef90f2..7cf9310de0ec 100644 > > > > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c > > > > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c > > > > @@ -723,7 +723,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned > > > > long gpa, struct kvm *kvm) > > > > > > > > dpage = pfn_to_page(uvmem_pfn); > > > > dpage->zone_device_data = pvt; > > > > - zone_device_page_init(dpage, 0); > > > > + zone_device_page_init(dpage, &kvmppc_uvmem_pgmap, 0); > > > > return dpage; > > > > out_clear: > > > > spin_lock(&kvmppc_uvmem_bitmap_lock); > > > > diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c > > > > b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c > > > > index af53e796ea1b..6ada7b4af7c6 100644 > > > > --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c > > > > +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c > > > > @@ -217,7 +217,7 @@ svm_migrate_get_vram_page(struct svm_range *prange, > > > > unsigned long pfn) > > > > page = pfn_to_page(pfn); > > > > svm_range_bo_ref(prange->svm_bo); > > > > page->zone_device_data = prange->svm_bo; > > > > - zone_device_page_init(page, 0); > > > > + zone_device_page_init(page, page_pgmap(page), 0); > > > > } > > > > > > > > static void > > > > diff --git a/drivers/gpu/drm/drm_pagemap.c > > > > b/drivers/gpu/drm/drm_pagemap.c > > > > index 03ee39a761a4..c497726b0147 100644 > > > > --- a/drivers/gpu/drm/drm_pagemap.c > > > > +++ b/drivers/gpu/drm/drm_pagemap.c > > > > @@ -201,7 +201,7 @@ static void drm_pagemap_get_devmem_page(struct page > > > > *page, > > > > struct drm_pagemap_zdd *zdd) > > > > { > > > > page->zone_device_data = drm_pagemap_zdd_get(zdd); > > > > - zone_device_page_init(page, 0); > > > > + zone_device_page_init(page, zdd->dpagemap->pagemap, 0); > > > > } > > > > > > > > /** > > > > diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c > > > > b/drivers/gpu/drm/nouveau/nouveau_dmem.c > > > > index 58071652679d..3d8031296eed 100644 > > > > --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c > > > > +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c > > > > @@ -425,7 +425,7 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm > > > > *drm, bool is_large) > > > > order = ilog2(DMEM_CHUNK_NPAGES); > > > > } > > > > > > > > - zone_device_folio_init(folio, order); > > > > + zone_device_folio_init(folio, page_pgmap(folio_page(folio, 0)), > > > > order); > > > > return page; > > > > } > > > > > > > > diff --git a/include/linux/memremap.h b/include/linux/memremap.h > > > > index 713ec0435b48..e3c2ccf872a8 100644 > > > > --- a/include/linux/memremap.h > > > > +++ b/include/linux/memremap.h > > > > @@ -224,7 +224,8 @@ static inline bool is_fsdax_page(const struct page > > > > *page) > > > > } > > > > > > > > #ifdef CONFIG_ZONE_DEVICE > > > > -void zone_device_page_init(struct page *page, unsigned int order); > > > > +void zone_device_page_init(struct page *page, struct dev_pagemap > > > > *pgmap, > > > > + unsigned int order); > > > > void *memremap_pages(struct dev_pagemap *pgmap, int nid); > > > > void memunmap_pages(struct dev_pagemap *pgmap); > > > > void *devm_memremap_pages(struct device *dev, struct dev_pagemap > > > > *pgmap); > > > > @@ -234,9 +235,11 @@ bool pgmap_pfn_valid(struct dev_pagemap *pgmap, > > > > unsigned long pfn); > > > > > > > > unsigned long memremap_compat_align(void); > > > > > > > > -static inline void zone_device_folio_init(struct folio *folio, > > > > unsigned int order) > > > > +static inline void zone_device_folio_init(struct folio *folio, > > > > + struct dev_pagemap *pgmap, > > > > + unsigned int order) > > > > { > > > > - zone_device_page_init(&folio->page, order); > > > > + zone_device_page_init(&folio->page, pgmap, order); > > > > if (order) > > > > folio_set_large_rmappable(folio); > > > > } > > > > diff --git a/lib/test_hmm.c b/lib/test_hmm.c > > > > index 8af169d3873a..455a6862ae50 100644 > > > > --- a/lib/test_hmm.c > > > > +++ b/lib/test_hmm.c > > > > @@ -662,7 +662,9 @@ static struct page > > > > *dmirror_devmem_alloc_page(struct dmirror *dmirror, > > > > goto error; > > > > } > > > > > > > > - zone_device_folio_init(page_folio(dpage), order); > > > > + zone_device_folio_init(page_folio(dpage), > > > > + page_pgmap(folio_page(page_folio(dpage), > > > > 0)), > > > > + order); > > > > dpage->zone_device_data = rpage; > > > > return dpage; > > > > > > > > diff --git a/mm/memremap.c b/mm/memremap.c > > > > index 63c6ab4fdf08..6f46ab14662b 100644 > > > > --- a/mm/memremap.c > > > > +++ b/mm/memremap.c > > > > @@ -477,10 +477,28 @@ void free_zone_device_folio(struct folio *folio) > > > > } > > > > } > > > > > > > > -void zone_device_page_init(struct page *page, unsigned int order) > > > > +void zone_device_page_init(struct page *page, struct dev_pagemap > > > > *pgmap, > > > > + unsigned int order) > > > > { > > > > + struct page *new_page = page; > > > > + unsigned int i; > > > > + > > > > VM_WARN_ON_ONCE(order > MAX_ORDER_NR_PAGES); > > > > > > > > + for (i = 0; i < (1UL << order); ++i, ++new_page) { > > > > + struct folio *new_folio = (struct folio *)new_page; > > > > + > > > > + new_page->flags.f &= ~0xffUL; /* Clear possible > > > > order, page head */ > > > > > > This seems odd to me, mainly due to the "magic" number. Why not just clear > > > the flags entirely? Or at least explicitly just clear the flags you care > > > about > > > which would remove the need for the comment and should let you use the > > > proper > > > PageFlag functions. > > > > > > > I'm copying this from folio_reset_order [1]. My paranoia about touching > > anything related to struct page is high, so I did the same thing > > folio_reset_order does here.
So why not just use folio_reset_order() below? > > > > [1] https://elixir.bootlin.com/linux/v6.18.5/source/include/linux/mm.h#L1075 > > > > This immediately hangs my first SVM test... > > diff --git a/mm/memremap.c b/mm/memremap.c > index 6f46ab14662b..ef8c56876cf5 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -488,7 +488,7 @@ void zone_device_page_init(struct page *page, struct > dev_pagemap *pgmap, > for (i = 0; i < (1UL << order); ++i, ++new_page) { > struct folio *new_folio = (struct folio *)new_page; > > - new_page->flags.f &= ~0xffUL; /* Clear possible order, page > head */ > + new_page->flags.f = 0; > #ifdef NR_PAGES_IN_LARGE_FOLIO > ((struct folio *)(new_page - 1))->_nr_pages = 0; This seems wrong to me - I saw your reply to Balbir but for an order-0 page isn't this going to access a completely different, possibly already allocated, page? > #endif > > I can walk through exactly which flags need to be cleared, but my > feeling is that likely any flag that the order field overloads and can > possibly encode should be cleared—so bits 0–7 based on the existing > code. > > How about in a follow-up we normalize setting / clearing the order flag > field with a #define and an inline helper? Ie: Would something like the following work: ClearPageHead(new_page); clear_compound_head(new_page); folio_reset_order(new_folio); Which would also deal with setting _nr_pages. > Matt > > > > > +#ifdef NR_PAGES_IN_LARGE_FOLIO > > > > + ((struct folio *)(new_page - 1))->_nr_pages = 0; > > > > +#endif > > > > + new_folio->mapping = NULL; > > > > + new_folio->pgmap = pgmap; /* Also clear compound > > > > head */ > > > > + new_folio->share = 0; /* fsdax only, unused for > > > > device private */ > > > > > > It would be nice if the FS DAX code actually used this as well. Is there a > > > reason that change was dropped from the series? > > > > > > > I don't have a test platform for FS DAX. In prior revisions, I was just > > moving existing FS DAX code to a helper, which I felt confident about. > > > > This revision is slightly different, and I don't feel comfortable > > modifying FS DAX code without a test platform. I agree we should update > > FS DAX, but that should be done in a follow-up with coordinated testing. Fair enough, I figured something like this might be your answer :-) You could update it and ask people with access to such a system to test it though (unfortunately my setup has bit-rotted beyond repair). But I'm ok leaving to for a future change. > > > > Matt > > > > > > + VM_WARN_ON_FOLIO(folio_ref_count(new_folio), new_folio); > > > > + VM_WARN_ON_FOLIO(!folio_is_zone_device(new_folio), > > > > new_folio); > > > > + } > > > > + > > > > /* > > > > * Drivers shouldn't be allocating pages after calling > > > > * memunmap_pages(). > > > > -- > > > > 2.43.0 > > > >
