From: Jérôme Glisse <jglisse@xxxxxxxxxx> Subject: mm/hmm/mirror: device page fault handler This handles page fault on behalf of device driver, unlike handle_mm_fault() it does not trigger migration back to system memory for device memory. Link: http://lkml.kernel.org/r/20170817000548.32038-6-jglisse@xxxxxxxxxx Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx> Signed-off-by: Evgeny Baskakov <ebaskakov@xxxxxxxxxx> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx> Signed-off-by: Mark Hairgrove <mhairgrove@xxxxxxxxxx> Signed-off-by: Sherry Cheung <SCheung@xxxxxxxxxx> Signed-off-by: Subhash Gutti <sgutti@xxxxxxxxxx> Cc: Aneesh Kumar <aneesh.kumar@xxxxxxxxxxxxxxxxxx> Cc: Balbir Singh <bsingharora@xxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: David Nellans <dnellans@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: Bob Liu <liubo95@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/hmm.h | 27 ++++ mm/hmm.c | 256 ++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 271 insertions(+), 12 deletions(-) diff -puN include/linux/hmm.h~mm-hmm-mirror-device-page-fault-handler include/linux/hmm.h --- a/include/linux/hmm.h~mm-hmm-mirror-device-page-fault-handler +++ a/include/linux/hmm.h @@ -292,6 +292,33 @@ int hmm_vma_get_pfns(struct vm_area_stru unsigned long end, hmm_pfn_t *pfns); bool hmm_vma_range_done(struct vm_area_struct *vma, struct hmm_range *range); + + +/* + * Fault memory on behalf of device driver. Unlike handle_mm_fault(), this will + * not migrate any device memory back to system memory. The hmm_pfn_t array will + * be updated with the fault result and current snapshot of the CPU page table + * for the range. + * + * The mmap_sem must be taken in read mode before entering and it might be + * dropped by the function if the block argument is false. In that case, the + * function returns -EAGAIN. + * + * Return value does not reflect if the fault was successful for every single + * address or not. Therefore, the caller must to inspect the hmm_pfn_t array to + * determine fault status for each address. + * + * Trying to fault inside an invalid vma will result in -EINVAL. + * + * See the function description in mm/hmm.c for further documentation. + */ +int hmm_vma_fault(struct vm_area_struct *vma, + struct hmm_range *range, + unsigned long start, + unsigned long end, + hmm_pfn_t *pfns, + bool write, + bool block); #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */ diff -puN mm/hmm.c~mm-hmm-mirror-device-page-fault-handler mm/hmm.c --- a/mm/hmm.c~mm-hmm-mirror-device-page-fault-handler +++ a/mm/hmm.c @@ -221,6 +221,36 @@ void hmm_mirror_unregister(struct hmm_mi } EXPORT_SYMBOL(hmm_mirror_unregister); +struct hmm_vma_walk { + struct hmm_range *range; + unsigned long last; + bool fault; + bool block; + bool write; +}; + +static int hmm_vma_do_fault(struct mm_walk *walk, + unsigned long addr, + hmm_pfn_t *pfn) +{ + unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_REMOTE; + struct hmm_vma_walk *hmm_vma_walk = walk->private; + struct vm_area_struct *vma = walk->vma; + int r; + + flags |= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY; + flags |= hmm_vma_walk->write ? FAULT_FLAG_WRITE : 0; + r = handle_mm_fault(vma, addr, flags); + if (r & VM_FAULT_RETRY) + return -EBUSY; + if (r & VM_FAULT_ERROR) { + *pfn = HMM_PFN_ERROR; + return -EFAULT; + } + + return -EAGAIN; +} + static void hmm_pfns_special(hmm_pfn_t *pfns, unsigned long addr, unsigned long end) @@ -244,34 +274,62 @@ static int hmm_pfns_bad(unsigned long ad return 0; } +static void hmm_pfns_clear(hmm_pfn_t *pfns, + unsigned long addr, + unsigned long end) +{ + for (; addr < end; addr += PAGE_SIZE, pfns++) + *pfns = 0; +} + static int hmm_vma_walk_hole(unsigned long addr, unsigned long end, struct mm_walk *walk) { - struct hmm_range *range = walk->private; + struct hmm_vma_walk *hmm_vma_walk = walk->private; + struct hmm_range *range = hmm_vma_walk->range; hmm_pfn_t *pfns = range->pfns; unsigned long i; + hmm_vma_walk->last = addr; i = (addr - range->start) >> PAGE_SHIFT; - for (; addr < end; addr += PAGE_SIZE, i++) + for (; addr < end; addr += PAGE_SIZE, i++) { pfns[i] = HMM_PFN_EMPTY; + if (hmm_vma_walk->fault) { + int ret; - return 0; + ret = hmm_vma_do_fault(walk, addr, &pfns[i]); + if (ret != -EAGAIN) + return ret; + } + } + + return hmm_vma_walk->fault ? -EAGAIN : 0; } static int hmm_vma_walk_clear(unsigned long addr, unsigned long end, struct mm_walk *walk) { - struct hmm_range *range = walk->private; + struct hmm_vma_walk *hmm_vma_walk = walk->private; + struct hmm_range *range = hmm_vma_walk->range; hmm_pfn_t *pfns = range->pfns; unsigned long i; + hmm_vma_walk->last = addr; i = (addr - range->start) >> PAGE_SHIFT; - for (; addr < end; addr += PAGE_SIZE, i++) + for (; addr < end; addr += PAGE_SIZE, i++) { pfns[i] = 0; + if (hmm_vma_walk->fault) { + int ret; - return 0; + ret = hmm_vma_do_fault(walk, addr, &pfns[i]); + if (ret != -EAGAIN) + return ret; + } + } + + return hmm_vma_walk->fault ? -EAGAIN : 0; } static int hmm_vma_walk_pmd(pmd_t *pmdp, @@ -279,15 +337,18 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, unsigned long end, struct mm_walk *walk) { - struct hmm_range *range = walk->private; + struct hmm_vma_walk *hmm_vma_walk = walk->private; + struct hmm_range *range = hmm_vma_walk->range; struct vm_area_struct *vma = walk->vma; hmm_pfn_t *pfns = range->pfns; unsigned long addr = start, i; + bool write_fault; hmm_pfn_t flag; pte_t *ptep; i = (addr - range->start) >> PAGE_SHIFT; flag = vma->vm_flags & VM_READ ? HMM_PFN_READ : 0; + write_fault = hmm_vma_walk->fault & hmm_vma_walk->write; again: if (pmd_none(*pmdp)) @@ -316,6 +377,9 @@ again: if (pmd_protnone(pmd)) return hmm_vma_walk_clear(start, end, walk); + if (write_fault && !pmd_write(pmd)) + return hmm_vma_walk_clear(start, end, walk); + pfn = pmd_pfn(pmd) + pte_index(addr); flag |= pmd_write(pmd) ? HMM_PFN_WRITE : 0; for (; addr < end; addr += PAGE_SIZE, i++, pfn++) @@ -332,13 +396,55 @@ again: pfns[i] = 0; - if (pte_none(pte) || !pte_present(pte)) { + if (pte_none(pte)) { pfns[i] = HMM_PFN_EMPTY; + if (hmm_vma_walk->fault) + goto fault; continue; } + if (!pte_present(pte)) { + swp_entry_t entry; + + if (!non_swap_entry(entry)) { + if (hmm_vma_walk->fault) + goto fault; + continue; + } + + entry = pte_to_swp_entry(pte); + + /* + * This is a special swap entry, ignore migration, use + * device and report anything else as error. + */ + if (is_migration_entry(entry)) { + if (hmm_vma_walk->fault) { + pte_unmap(ptep); + hmm_vma_walk->last = addr; + migration_entry_wait(vma->vm_mm, + pmdp, addr); + return -EAGAIN; + } + continue; + } else { + /* Report error for everything else */ + pfns[i] = HMM_PFN_ERROR; + } + continue; + } + + if (write_fault && !pte_write(pte)) + goto fault; + pfns[i] = hmm_pfn_t_from_pfn(pte_pfn(pte)) | flag; pfns[i] |= pte_write(pte) ? HMM_PFN_WRITE : 0; + continue; + +fault: + pte_unmap(ptep); + /* Fault all pages in range */ + return hmm_vma_walk_clear(start, end, walk); } pte_unmap(ptep - 1); @@ -371,6 +477,7 @@ int hmm_vma_get_pfns(struct vm_area_stru unsigned long end, hmm_pfn_t *pfns) { + struct hmm_vma_walk hmm_vma_walk; struct mm_walk mm_walk; struct hmm *hmm; @@ -402,9 +509,12 @@ int hmm_vma_get_pfns(struct vm_area_stru list_add_rcu(&range->list, &hmm->ranges); spin_unlock(&hmm->lock); + hmm_vma_walk.fault = false; + hmm_vma_walk.range = range; + mm_walk.private = &hmm_vma_walk; + mm_walk.vma = vma; mm_walk.mm = vma->vm_mm; - mm_walk.private = range; mm_walk.pte_entry = NULL; mm_walk.test_walk = NULL; mm_walk.hugetlb_entry = NULL; @@ -412,7 +522,6 @@ int hmm_vma_get_pfns(struct vm_area_stru mm_walk.pte_hole = hmm_vma_walk_hole; walk_page_range(start, end, &mm_walk); - return 0; } EXPORT_SYMBOL(hmm_vma_get_pfns); @@ -439,7 +548,7 @@ EXPORT_SYMBOL(hmm_vma_get_pfns); * * There are two ways to use this : * again: - * hmm_vma_get_pfns(vma, range, start, end, pfns); + * hmm_vma_get_pfns(vma, range, start, end, pfns); or hmm_vma_fault(...); * trans = device_build_page_table_update_transaction(pfns); * device_page_table_lock(); * if (!hmm_vma_range_done(vma, range)) { @@ -450,7 +559,7 @@ EXPORT_SYMBOL(hmm_vma_get_pfns); * device_page_table_unlock(); * * Or: - * hmm_vma_get_pfns(vma, range, start, end, pfns); + * hmm_vma_get_pfns(vma, range, start, end, pfns); or hmm_vma_fault(...); * device_page_table_lock(); * hmm_vma_range_done(vma, range); * device_update_page_table(pfns); @@ -479,4 +588,127 @@ bool hmm_vma_range_done(struct vm_area_s return range->valid; } EXPORT_SYMBOL(hmm_vma_range_done); + +/* + * hmm_vma_fault() - try to fault some address in a virtual address range + * @vma: virtual memory area containing the virtual address range + * @range: use to track pfns array content validity + * @start: fault range virtual start address (inclusive) + * @end: fault range virtual end address (exclusive) + * @pfns: array of hmm_pfn_t, only entry with fault flag set will be faulted + * @write: is it a write fault + * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem) + * Returns: 0 success, error otherwise (-EAGAIN means mmap_sem have been drop) + * + * This is similar to a regular CPU page fault except that it will not trigger + * any memory migration if the memory being faulted is not accessible by CPUs. + * + * On error, for one virtual address in the range, the function will set the + * hmm_pfn_t error flag for the corresponding pfn entry. + * + * Expected use pattern: + * retry: + * down_read(&mm->mmap_sem); + * // Find vma and address device wants to fault, initialize hmm_pfn_t + * // array accordingly + * ret = hmm_vma_fault(vma, start, end, pfns, allow_retry); + * switch (ret) { + * case -EAGAIN: + * hmm_vma_range_done(vma, range); + * // You might want to rate limit or yield to play nicely, you may + * // also commit any valid pfn in the array assuming that you are + * // getting true from hmm_vma_range_monitor_end() + * goto retry; + * case 0: + * break; + * default: + * // Handle error ! + * up_read(&mm->mmap_sem) + * return; + * } + * // Take device driver lock that serialize device page table update + * driver_lock_device_page_table_update(); + * hmm_vma_range_done(vma, range); + * // Commit pfns we got from hmm_vma_fault() + * driver_unlock_device_page_table_update(); + * up_read(&mm->mmap_sem) + * + * YOU MUST CALL hmm_vma_range_done() AFTER THIS FUNCTION RETURN SUCCESS (0) + * BEFORE FREEING THE range struct OR YOU WILL HAVE SERIOUS MEMORY CORRUPTION ! + * + * YOU HAVE BEEN WARNED ! + */ +int hmm_vma_fault(struct vm_area_struct *vma, + struct hmm_range *range, + unsigned long start, + unsigned long end, + hmm_pfn_t *pfns, + bool write, + bool block) +{ + struct hmm_vma_walk hmm_vma_walk; + struct mm_walk mm_walk; + struct hmm *hmm; + int ret; + + /* Sanity check, this really should not happen ! */ + if (start < vma->vm_start || start >= vma->vm_end) + return -EINVAL; + if (end < vma->vm_start || end > vma->vm_end) + return -EINVAL; + + hmm = hmm_register(vma->vm_mm); + if (!hmm) { + hmm_pfns_clear(pfns, start, end); + return -ENOMEM; + } + /* Caller must have registered a mirror using hmm_mirror_register() */ + if (!hmm->mmu_notifier.ops) + return -EINVAL; + + /* Initialize range to track CPU page table update */ + range->start = start; + range->pfns = pfns; + range->end = end; + spin_lock(&hmm->lock); + range->valid = true; + list_add_rcu(&range->list, &hmm->ranges); + spin_unlock(&hmm->lock); + + /* FIXME support hugetlb fs */ + if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) { + hmm_pfns_special(pfns, start, end); + return 0; + } + + hmm_vma_walk.fault = true; + hmm_vma_walk.write = write; + hmm_vma_walk.block = block; + hmm_vma_walk.range = range; + mm_walk.private = &hmm_vma_walk; + hmm_vma_walk.last = range->start; + + mm_walk.vma = vma; + mm_walk.mm = vma->vm_mm; + mm_walk.pte_entry = NULL; + mm_walk.test_walk = NULL; + mm_walk.hugetlb_entry = NULL; + mm_walk.pmd_entry = hmm_vma_walk_pmd; + mm_walk.pte_hole = hmm_vma_walk_hole; + + do { + ret = walk_page_range(start, end, &mm_walk); + start = hmm_vma_walk.last; + } while (ret == -EAGAIN); + + if (ret) { + unsigned long i; + + i = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT; + hmm_pfns_clear(&pfns[i], hmm_vma_walk.last, end); + hmm_vma_range_done(vma, range); + } + return ret; +} +EXPORT_SYMBOL(hmm_vma_fault); #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */ _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
