From: Alistair Popple <apopple@xxxxxxxxxx> Subject: mm: remove special swap entry functions Patch series "Add support for SVM atomics in Nouveau", v11. Introduction ============ Some devices have features such as atomic PTE bits that can be used to implement atomic access to system memory. To support atomic operations to a shared virtual memory page such a device needs access to that page which is exclusive of the CPU. This series introduces a mechanism to temporarily unmap pages granting exclusive access to a device. These changes are required to support OpenCL atomic operations in Nouveau to shared virtual memory (SVM) regions allocated with the CL_MEM_SVM_ATOMICS clSVMAlloc flag. A more complete description of the OpenCL SVM feature is available at https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/ OpenCL_API.html#_shared_virtual_memory . Implementation ============== Exclusive device access is implemented by adding a new swap entry type (SWAP_DEVICE_EXCLUSIVE) which is similar to a migration entry. The main difference is that on fault the original entry is immediately restored by the fault handler instead of waiting. Restoring the entry triggers calls to MMU notifers which allows a device driver to revoke the atomic access permission from the GPU prior to the CPU finalising the entry. Patches ======= Patches 1 & 2 refactor existing migration and device private entry functions. Patches 3 & 4 rework try_to_unmap_one() by splitting out unrelated functionality into separate functions - try_to_migrate_one() and try_to_munlock_one(). Patch 5 renames some existing code but does not introduce functionality. Patch 6 is a small clean-up to swap entry handling in copy_pte_range(). Patch 7 contains the bulk of the implementation for device exclusive memory. Patch 8 contains some additions to the HMM selftests to ensure everything works as expected. Patch 9 is a cleanup for the Nouveau SVM implementation. Patch 10 contains the implementation of atomic access for the Nouveau driver. Testing ======= This has been tested with upstream Mesa 21.1.0 and a simple OpenCL program which checks that GPU atomic accesses to system memory are atomic. Without this series the test fails as there is no way of write-protecting the page mapping which results in the device clobbering CPU writes. For reference the test is available at https://ozlabs.org/~apopple/opencl_svm_atomics/ Further testing has been performed by adding support for testing exclusive access to the hmm-tests kselftests. This patch (of 10): Remove multiple similar inline functions for dealing with different types of special swap entries. Both migration and device private swap entries use the swap offset to store a pfn. Instead of multiple inline functions to obtain a struct page for each swap entry type use a common function pfn_swap_entry_to_page(). Also open-code the various entry_to_pfn() functions as this results is shorter code that is easier to understand. Link: https://lkml.kernel.org/r/20210616105937.23201-1-apopple@xxxxxxxxxx Link: https://lkml.kernel.org/r/20210616105937.23201-2-apopple@xxxxxxxxxx Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> Reviewed-by: Ralph Campbell <rcampbell@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Ben Skeggs <bskeggs@xxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/s390/mm/pgtable.c | 2 - fs/proc/task_mmu.c | 23 ++++-------- include/linux/swap.h | 4 +- include/linux/swapops.h | 69 ++++++++++++-------------------------- mm/hmm.c | 5 +- mm/huge_memory.c | 6 +-- mm/memcontrol.c | 2 - mm/memory.c | 10 ++--- mm/migrate.c | 6 +-- mm/page_vma_mapped.c | 6 +-- 10 files changed, 51 insertions(+), 82 deletions(-) --- a/arch/s390/mm/pgtable.c~mm-remove-special-swap-entry-functions +++ a/arch/s390/mm/pgtable.c @@ -691,7 +691,7 @@ static void ptep_zap_swap_entry(struct m if (!non_swap_entry(entry)) dec_mm_counter(mm, MM_SWAPENTS); else if (is_migration_entry(entry)) { - struct page *page = migration_entry_to_page(entry); + struct page *page = pfn_swap_entry_to_page(entry); dec_mm_counter(mm, mm_counter(page)); } --- a/fs/proc/task_mmu.c~mm-remove-special-swap-entry-functions +++ a/fs/proc/task_mmu.c @@ -514,10 +514,8 @@ static void smaps_pte_entry(pte_t *pte, } else { mss->swap_pss += (u64)PAGE_SIZE << PSS_SHIFT; } - } else if (is_migration_entry(swpent)) - page = migration_entry_to_page(swpent); - else if (is_device_private_entry(swpent)) - page = device_private_entry_to_page(swpent); + } else if (is_pfn_swap_entry(swpent)) + page = pfn_swap_entry_to_page(swpent); } else if (unlikely(IS_ENABLED(CONFIG_SHMEM) && mss->check_shmem_swap && pte_none(*pte))) { page = xa_load(&vma->vm_file->f_mapping->i_pages, @@ -549,7 +547,7 @@ static void smaps_pmd_entry(pmd_t *pmd, swp_entry_t entry = pmd_to_swp_entry(*pmd); if (is_migration_entry(entry)) - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); } if (IS_ERR_OR_NULL(page)) return; @@ -694,10 +692,8 @@ static int smaps_hugetlb_range(pte_t *pt } else if (is_swap_pte(*pte)) { swp_entry_t swpent = pte_to_swp_entry(*pte); - if (is_migration_entry(swpent)) - page = migration_entry_to_page(swpent); - else if (is_device_private_entry(swpent)) - page = device_private_entry_to_page(swpent); + if (is_pfn_swap_entry(swpent)) + page = pfn_swap_entry_to_page(swpent); } if (page) { int mapcount = page_mapcount(page); @@ -1389,11 +1385,8 @@ static pagemap_entry_t pte_to_pagemap_en frame = swp_type(entry) | (swp_offset(entry) << MAX_SWAPFILES_SHIFT); flags |= PM_SWAP; - if (is_migration_entry(entry)) - page = migration_entry_to_page(entry); - - if (is_device_private_entry(entry)) - page = device_private_entry_to_page(entry); + if (is_pfn_swap_entry(entry)) + page = pfn_swap_entry_to_page(entry); } if (page && !PageAnon(page)) @@ -1454,7 +1447,7 @@ static int pagemap_pmd_range(pmd_t *pmdp if (pmd_swp_uffd_wp(pmd)) flags |= PM_UFFD_WP; VM_BUG_ON(!is_pmd_migration_entry(pmd)); - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); } #endif --- a/include/linux/swap.h~mm-remove-special-swap-entry-functions +++ a/include/linux/swap.h @@ -564,8 +564,8 @@ static inline void show_swap_cache_info( { } -#define free_swap_and_cache(e) ({(is_migration_entry(e) || is_device_private_entry(e));}) -#define swapcache_prepare(e) ({(is_migration_entry(e) || is_device_private_entry(e));}) +/* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */ +#define free_swap_and_cache(e) is_pfn_swap_entry(e) static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask) { --- a/include/linux/swapops.h~mm-remove-special-swap-entry-functions +++ a/include/linux/swapops.h @@ -128,16 +128,6 @@ static inline bool is_write_device_priva { return unlikely(swp_type(entry) == SWP_DEVICE_WRITE); } - -static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry) -{ - return swp_offset(entry); -} - -static inline struct page *device_private_entry_to_page(swp_entry_t entry) -{ - return pfn_to_page(swp_offset(entry)); -} #else /* CONFIG_DEVICE_PRIVATE */ static inline swp_entry_t make_device_private_entry(struct page *page, bool write) { @@ -157,16 +147,6 @@ static inline bool is_write_device_priva { return false; } - -static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry) -{ - return 0; -} - -static inline struct page *device_private_entry_to_page(swp_entry_t entry) -{ - return NULL; -} #endif /* CONFIG_DEVICE_PRIVATE */ #ifdef CONFIG_MIGRATION @@ -189,22 +169,6 @@ static inline int is_write_migration_ent return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE); } -static inline unsigned long migration_entry_to_pfn(swp_entry_t entry) -{ - return swp_offset(entry); -} - -static inline struct page *migration_entry_to_page(swp_entry_t entry) -{ - struct page *p = pfn_to_page(swp_offset(entry)); - /* - * Any use of migration entries may only occur while the - * corresponding page is locked - */ - BUG_ON(!PageLocked(compound_head(p))); - return p; -} - static inline void make_migration_entry_read(swp_entry_t *entry) { *entry = swp_entry(SWP_MIGRATION_READ, swp_offset(*entry)); @@ -224,16 +188,6 @@ static inline int is_migration_entry(swp return 0; } -static inline unsigned long migration_entry_to_pfn(swp_entry_t entry) -{ - return 0; -} - -static inline struct page *migration_entry_to_page(swp_entry_t entry) -{ - return NULL; -} - static inline void make_migration_entry_read(swp_entry_t *entryp) { } static inline void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep, spinlock_t *ptl) { } @@ -248,6 +202,29 @@ static inline int is_write_migration_ent #endif +static inline struct page *pfn_swap_entry_to_page(swp_entry_t entry) +{ + struct page *p = pfn_to_page(swp_offset(entry)); + + /* + * Any use of migration entries may only occur while the + * corresponding page is locked + */ + BUG_ON(is_migration_entry(entry) && !PageLocked(p)); + + return p; +} + +/* + * A pfn swap entry is a special type of swap entry that always has a pfn stored + * in the swap offset. They are used to represent unaddressable device memory + * and to restrict access to a page undergoing migration. + */ +static inline bool is_pfn_swap_entry(swp_entry_t entry) +{ + return is_migration_entry(entry) || is_device_private_entry(entry); +} + struct page_vma_mapped_walk; #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION --- a/mm/hmm.c~mm-remove-special-swap-entry-functions +++ a/mm/hmm.c @@ -214,7 +214,7 @@ static inline bool hmm_is_device_private swp_entry_t entry) { return is_device_private_entry(entry) && - device_private_entry_to_page(entry)->pgmap->owner == + pfn_swap_entry_to_page(entry)->pgmap->owner == range->dev_private_owner; } @@ -257,8 +257,7 @@ static int hmm_vma_handle_pte(struct mm_ cpu_flags = HMM_PFN_VALID; if (is_write_device_private_entry(entry)) cpu_flags |= HMM_PFN_WRITE; - *hmm_pfn = device_private_entry_to_pfn(entry) | - cpu_flags; + *hmm_pfn = swp_offset(entry) | cpu_flags; return 0; } --- a/mm/huge_memory.c~mm-remove-special-swap-entry-functions +++ a/mm/huge_memory.c @@ -1643,7 +1643,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, VM_BUG_ON(!is_pmd_migration_entry(orig_pmd)); entry = pmd_to_swp_entry(orig_pmd); - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); flush_needed = 0; } else WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); @@ -2012,7 +2012,7 @@ static void __split_huge_pmd_locked(stru swp_entry_t entry; entry = pmd_to_swp_entry(old_pmd); - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); } else { page = pmd_page(old_pmd); if (!PageDirty(page) && pmd_dirty(old_pmd)) @@ -2066,7 +2066,7 @@ static void __split_huge_pmd_locked(stru swp_entry_t entry; entry = pmd_to_swp_entry(old_pmd); - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); write = is_write_migration_entry(entry); young = false; soft_dirty = pmd_swp_soft_dirty(old_pmd); --- a/mm/memcontrol.c~mm-remove-special-swap-entry-functions +++ a/mm/memcontrol.c @@ -5532,7 +5532,7 @@ static struct page *mc_handle_swap_pte(s * as special swap entry in the CPU page table. */ if (is_device_private_entry(ent)) { - page = device_private_entry_to_page(ent); + page = pfn_swap_entry_to_page(ent); /* * MEMORY_DEVICE_PRIVATE means ZONE_DEVICE page and which have * a refcount of 1 when free (unlike normal page) --- a/mm/memory.c~mm-remove-special-swap-entry-functions +++ a/mm/memory.c @@ -729,7 +729,7 @@ copy_nonpresent_pte(struct mm_struct *ds } rss[MM_SWAPENTS]++; } else if (is_migration_entry(entry)) { - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); rss[mm_counter(page)]++; @@ -748,7 +748,7 @@ copy_nonpresent_pte(struct mm_struct *ds set_pte_at(src_mm, addr, src_pte, pte); } } else if (is_device_private_entry(entry)) { - page = device_private_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); /* * Update rss count even for unaddressable pages, as @@ -1280,7 +1280,7 @@ again: entry = pte_to_swp_entry(ptent); if (is_device_private_entry(entry)) { - struct page *page = device_private_entry_to_page(entry); + struct page *page = pfn_swap_entry_to_page(entry); if (unlikely(details && details->check_mapping)) { /* @@ -1309,7 +1309,7 @@ again: else if (is_migration_entry(entry)) { struct page *page; - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); rss[mm_counter(page)]--; } if (unlikely(!free_swap_and_cache(entry))) @@ -3372,7 +3372,7 @@ vm_fault_t do_swap_page(struct vm_fault migration_entry_wait(vma->vm_mm, vmf->pmd, vmf->address); } else if (is_device_private_entry(entry)) { - vmf->page = device_private_entry_to_page(entry); + vmf->page = pfn_swap_entry_to_page(entry); ret = vmf->page->pgmap->ops->migrate_to_ram(vmf); } else if (is_hwpoison_entry(entry)) { ret = VM_FAULT_HWPOISON; --- a/mm/migrate.c~mm-remove-special-swap-entry-functions +++ a/mm/migrate.c @@ -296,7 +296,7 @@ void __migration_entry_wait(struct mm_st if (!is_migration_entry(entry)) goto out; - page = migration_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); page = compound_head(page); /* @@ -337,7 +337,7 @@ void pmd_migration_entry_wait(struct mm_ ptl = pmd_lock(mm, pmd); if (!is_pmd_migration_entry(*pmd)) goto unlock; - page = migration_entry_to_page(pmd_to_swp_entry(*pmd)); + page = pfn_swap_entry_to_page(pmd_to_swp_entry(*pmd)); if (!get_page_unless_zero(page)) goto unlock; spin_unlock(ptl); @@ -2289,7 +2289,7 @@ again: if (!is_device_private_entry(entry)) goto next; - page = device_private_entry_to_page(entry); + page = pfn_swap_entry_to_page(entry); if (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_PRIVATE) || page->pgmap->owner != migrate->pgmap_owner) --- a/mm/page_vma_mapped.c~mm-remove-special-swap-entry-functions +++ a/mm/page_vma_mapped.c @@ -96,7 +96,7 @@ static bool check_pte(struct page_vma_ma if (!is_migration_entry(entry)) return false; - pfn = migration_entry_to_pfn(entry); + pfn = swp_offset(entry); } else if (is_swap_pte(*pvmw->pte)) { swp_entry_t entry; @@ -105,7 +105,7 @@ static bool check_pte(struct page_vma_ma if (!is_device_private_entry(entry)) return false; - pfn = device_private_entry_to_pfn(entry); + pfn = swp_offset(entry); } else { if (!pte_present(*pvmw->pte)) return false; @@ -233,7 +233,7 @@ restart: return not_found(pvmw); entry = pmd_to_swp_entry(pmde); if (!is_migration_entry(entry) || - migration_entry_to_page(entry) != page) + pfn_swap_entry_to_page(entry) != page) return not_found(pvmw); return true; } _
