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This >>> allocated physical address range is then remapped as device private >>> memory using memremap_pages(). >>> >>> Needing allocation of physical address space has some problems: >>> >>> 1) There may be insufficient physical address space to represent the >>> device memory. KASLR reducing the physical address space and VM >>> configurations with limited physical address space increase the >>> likelihood of hitting this especially as device memory increases.= This >>> has been observed to prevent device private from being initialize= d. >>> >>> 2) Attempting to add the device private pages to the linear map at >>> addresses beyond the actual physical memory causes issues on >>> architectures like aarch64 meaning the feature does not work ther= e. >>> >>> Instead of using the physical address space, introduce a device private >>> address space and allocate devices regions from there to represent the >>> device private pages. >>> >>> Introduce a new interface memremap_device_private_pagemap() that >>> allocates a requested amount of device private address space and create= s >>> the necessary device private pages. >>> >>> To support this new interface, struct dev_pagemap needs some changes: >>> >>> - Add a new dev_pagemap::nr_pages field as an input parameter. >>> - Add a new dev_pagemap::pages array to store the device >>> private pages. >>> >>> When using memremap_device_private_pagemap(), rather then passing in >>> dev_pagemap::ranges[dev_pagemap::nr_ranges] of physical address space t= o >>> be remapped, dev_pagemap::nr_ranges will always be 1, and the device >>> private range that is reserved is returned in dev_pagemap::range. >>> >>> Forbid calling memremap_pages() with dev_pagemap::ranges::type =3D >>> MEMORY_DEVICE_PRIVATE. >>> >>> Represent this device private address space using a new >>> device_private_pgmap_tree maple tree. This tree maps a given device >>> private address to a struct dev_pagemap, where a specific device privat= e >>> page may then be looked up in that dev_pagemap::pages array. >>> >>> Device private address space can be reclaimed and the assoicated device >>> private pages freed using the corresponding new >>> memunmap_device_private_pagemap() interface. >>> >>> Because the device private pages now live outside the physical address >>> space, they no longer have a normal PFN. This means that page_to_pfn(), >>> et al. are no longer meaningful. >>> >>> Introduce helpers: >>> >>> - device_private_page_to_offset() >>> - device_private_folio_to_offset() >>> >>> to take a given device private page / folio and return its offset withi= n >>> the device private address space. >>> >>> Update the places where we previously converted a device private page t= o >>> a PFN to use these new helpers. When we encounter a device private >>> offset, instead of looking up its page within the pagemap use >>> device_private_offset_to_page() instead. >>> >>> Update the existing users: >>> >>> - lib/test_hmm.c >>> - ppc ultravisor >>> - drm/amd/amdkfd >>> - gpu/drm/xe >>> - gpu/drm/nouveau >>> >>> to use the new memremap_device_private_pagemap() interface. >>> >>> Signed-off-by: Jordan Niethe >>> Signed-off-by: Alistair Popple >>> >>> --- >>> >>> NOTE: The updates to the existing drivers have only been compile tested= . >>> I'll need some help in testing these drivers. >>> >>> v1: >>> - Include NUMA node paramater for memremap_device_private_pagemap() >>> - Add devm_memremap_device_private_pagemap() and friends >>> - Update existing users of memremap_pages(): >>> - ppc ultravisor >>> - drm/amd/amdkfd >>> - gpu/drm/xe >>> - gpu/drm/nouveau >>> - Update for HMM huge page support >>> - Guard device_private_offset_to_page and friends with CONFIG_ZONE_DEVI= CE >>> >>> v2: >>> - Make sure last member of struct dev_pagemap remains DECLARE_FLEX_ARRA= Y(struct range, ranges); >>> --- >>> Documentation/mm/hmm.rst | 11 +- >>> arch/powerpc/kvm/book3s_hv_uvmem.c | 41 ++--- >>> drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 23 +-- >>> drivers/gpu/drm/nouveau/nouveau_dmem.c | 35 ++-- >>> drivers/gpu/drm/xe/xe_svm.c | 28 +--- >>> include/linux/hmm.h | 3 + >>> include/linux/leafops.h | 16 +- >>> include/linux/memremap.h | 64 +++++++- >>> include/linux/migrate.h | 6 +- >>> include/linux/mm.h | 2 + >>> include/linux/rmap.h | 5 +- >>> include/linux/swapops.h | 10 +- >>> lib/test_hmm.c | 69 ++++---- >>> mm/debug.c | 9 +- >>> mm/memremap.c | 193 ++++++++++++++++++----= - >>> mm/mm_init.c | 8 +- >>> mm/page_vma_mapped.c | 19 ++- >>> mm/rmap.c | 43 +++-- >>> mm/util.c | 5 +- >>> 19 files changed, 391 insertions(+), 199 deletions(-) >>> >> >> >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index e65329e1969f..b36599ab41ba 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -2038,6 +2038,8 @@ static inline unsigned long memdesc_section(memde= sc_flags_t mdf) >>> */ >>> static inline unsigned long folio_pfn(const struct folio *folio) >>> { >>> + VM_BUG_ON(folio_is_device_private(folio)); >> >> Please use VM_WARN_ON instead. > > ack. > >> >>> + >>> return page_to_pfn(&folio->page); >>> } >>> >>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >>> index 57c63b6a8f65..c1561a92864f 100644 >>> --- a/include/linux/rmap.h >>> +++ b/include/linux/rmap.h >>> @@ -951,7 +951,7 @@ static inline unsigned long page_vma_walk_pfn(unsig= ned long pfn) >>> static inline unsigned long folio_page_vma_walk_pfn(const struct foli= o *folio) >>> { >>> if (folio_is_device_private(folio)) >>> - return page_vma_walk_pfn(folio_pfn(folio)) | >>> + return page_vma_walk_pfn(device_private_folio_to_offset(folio)) | >>> PVMW_PFN_DEVICE_PRIVATE; >>> >>> return page_vma_walk_pfn(folio_pfn(folio)); >>> @@ -959,6 +959,9 @@ static inline unsigned long folio_page_vma_walk_pfn= (const struct folio *folio) >>> >>> static inline struct page *page_vma_walk_pfn_to_page(unsigned long pv= mw_pfn) >>> { >>> + if (pvmw_pfn & PVMW_PFN_DEVICE_PRIVATE) >>> + return device_private_offset_to_page(pvmw_pfn >> PVMW_PFN_SHIFT); >>> + >>> return pfn_to_page(pvmw_pfn >> PVMW_PFN_SHIFT); >>> } >> >> >> >>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >>> index 96c525785d78..141fe5abd33f 100644 >>> --- a/mm/page_vma_mapped.c >>> +++ b/mm/page_vma_mapped.c >>> @@ -107,6 +107,7 @@ static bool map_pte(struct page_vma_mapped_walk *pv= mw, pmd_t *pmdvalp, >>> static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned lon= g pte_nr) >>> { >>> unsigned long pfn; >>> + bool device_private =3D false; >>> pte_t ptent =3D ptep_get(pvmw->pte); >>> >>> if (pvmw->flags & PVMW_MIGRATION) { >>> @@ -115,6 +116,9 @@ static bool check_pte(struct page_vma_mapped_walk *= pvmw, unsigned long pte_nr) >>> if (!softleaf_is_migration(entry)) >>> return false; >>> >>> + if (softleaf_is_migration_device_private(entry)) >>> + device_private =3D true; >>> + >>> pfn =3D softleaf_to_pfn(entry); >>> } else if (pte_present(ptent)) { >>> pfn =3D pte_pfn(ptent); >>> @@ -127,8 +131,14 @@ static bool check_pte(struct page_vma_mapped_walk = *pvmw, unsigned long pte_nr) >>> return false; >>> >>> pfn =3D softleaf_to_pfn(entry); >>> + >>> + if (softleaf_is_device_private(entry)) >>> + device_private =3D true; >>> } >>> >>> + if ((device_private) ^ !!(pvmw->pfn & PVMW_PFN_DEVICE_PRIVATE)) >>> + return false; >>> + >>> if ((pfn + pte_nr - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT)) >>> return false; >>> if (pfn > ((pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1)) >>> @@ -137,8 +147,11 @@ static bool check_pte(struct page_vma_mapped_walk = *pvmw, unsigned long pte_nr) >>> } >>> >>> /* Returns true if the two ranges overlap. Careful to not overflow. = */ >>> -static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *= pvmw) >>> +static bool check_pmd(unsigned long pfn, bool device_private, struct p= age_vma_mapped_walk *pvmw) >>> { >>> + if ((device_private) ^ !!(pvmw->pfn & PVMW_PFN_DEVICE_PRIVATE)) >>> + return false; >>> + >>> if ((pfn + HPAGE_PMD_NR - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT)) >>> return false; >>> if (pfn > (pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1) >>> @@ -255,6 +268,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_wa= lk *pvmw) >>> >>> if (!softleaf_is_migration(entry) || >>> !check_pmd(softleaf_to_pfn(entry), >>> + softleaf_is_device_private(entry) || >>> + softleaf_is_migration_device_private(entry), >>> pvmw)) >>> return not_found(pvmw); >>> return true; >>> @@ -262,7 +277,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_wa= lk *pvmw) >>> if (likely(pmd_trans_huge(pmde))) { >>> if (pvmw->flags & PVMW_MIGRATION) >>> return not_found(pvmw); >>> - if (!check_pmd(pmd_pfn(pmde), pvmw)) >>> + if (!check_pmd(pmd_pfn(pmde), false, pvmw)) >>> return not_found(pvmw); >>> return true; >>> } >> >> It seems to me that you can add a new flag like =E2=80=9Cbool is_device_= private=E2=80=9D to >> indicate whether pfn is a device private index instead of pfn without >> manipulating pvmw->pfn itself. > > We could do it like that, however my concern with using a new param was t= hat > storing this info seperately might make it easier to misuse a device priv= ate > index as a regular pfn. > > It seemed like it could be easy to overlook both when creating the pvmw a= nd > then when accessing the pfn. That is why I asked for a helper function like page_vma_walk_pfn(pvmw) to return the converted pfn instead of pvmw->pfn directly. You can add a comme= nt to ask people to use helper function and even mark pvmw->pfn /* do not use directly */. In addition, your patch manipulates pfn by left shifting it by 1. Are you s= ure there is no weird arch having pfns with bit 63 being 1? Your change could break it, right? Best Regards, Yan, Zi