Sometimes immediately hard offlining a large chunk of contigous memory having uncorrected memory errors (UE) may not be the best option. Cloud providers usually serve capacity- and performance-critical guest memory with 1G HugeTLB hugepages, as this significantly reduces the overhead associated with managing page tables and TLB misses. However, for today's HugeTLB system, once a byte of memory in a hugepage is hardware corrupted, the kernel discards the whole hugepage, including the healthy portion. Customer workload running in the VM can hardly recover from such a great loss of memory. Therefore keeping or discarding a large chunk of contiguous memory owned by userspace (particularly to serve guest memory) due to recoverable UE may better be controlled by userspace process that owns the memory, e.g. VMM in Cloud environment. Introduce a memfd-based userspace memory failure (MFR) policy, MFD_MF_KEEP_UE_MAPPED. It is intended to be supported for other memfd, but the current implementation only covers HugeTLB. For any hugepage associated with the MFD_MF_KEEP_UE_MAPPED enabled memfd, whenever it runs into a UE, MFR doesn't hard offline the HWPoison-ed huge folio. IOW the HWPoison-ed memory remains accessible via the memory mapping created with that memfd. MFR still sends SIGBUS to the process as required. MFR also still maintains HWPoison metadata for the hugepage having the UE. A HWPoison-ed hugepage will be immediately isolated and prevented from future allocation once userspace truncates it via the memfd, or the owning memfd is closed. By default MFD_MF_KEEP_UE_MAPPED is not set, and MFR hard offlines hugepages having UEs. Tested with selftest in the follow-up commit. Signed-off-by: Jiaqi Yan Tested-by: William Roche --- fs/hugetlbfs/inode.c | 25 +++++++- include/linux/hugetlb.h | 7 +++ include/linux/pagemap.h | 24 +++++++ include/uapi/linux/memfd.h | 6 ++ mm/hugetlb.c | 20 +++++- mm/memfd.c | 15 ++++- mm/memory-failure.c | 124 +++++++++++++++++++++++++++++++++---- 7 files changed, 202 insertions(+), 19 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index f42548ee9083c..f8a5aa091d51d 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -532,6 +532,18 @@ static bool remove_inode_single_folio(struct hstate *h, struct inode *inode, } folio_unlock(folio); + + /* + * There may be pending HWPoison-ed folios when a memfd is being + * removed or part of it is being truncated. + * + * HugeTLBFS' error_remove_folio keeps the HWPoison-ed folios in + * page cache until mm wants to drop the folio at the end of the + * of the filemap. At this point, if memory failure was delayed + * by MFD_MF_KEEP_UE_MAPPED in the past, we can now deal with it. + */ + filemap_offline_hwpoison_folio(mapping, folio); + return ret; } @@ -563,13 +575,13 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, const pgoff_t end = lend >> PAGE_SHIFT; struct folio_batch fbatch; pgoff_t next, index; - int i, freed = 0; + int i, j, freed = 0; bool truncate_op = (lend == LLONG_MAX); folio_batch_init(&fbatch); next = lstart >> PAGE_SHIFT; while (filemap_get_folios(mapping, &next, end - 1, &fbatch)) { - for (i = 0; i < folio_batch_count(&fbatch); ++i) { + for (i = 0, j = 0; i < folio_batch_count(&fbatch); ++i) { struct folio *folio = fbatch.folios[i]; u32 hash = 0; @@ -584,8 +596,17 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, index, truncate_op)) freed++; + /* + * Skip HWPoison-ed hugepages, which should no + * longer be hugetlb if successfully dissolved. + */ + if (folio_test_hugetlb(folio)) + fbatch.folios[j++] = folio; + mutex_unlock(&hugetlb_fault_mutex_table[hash]); } + fbatch.nr = j; + folio_batch_release(&fbatch); cond_resched(); } diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 8e63e46b8e1f0..b7733ef5ee917 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -871,10 +871,17 @@ int dissolve_free_hugetlb_folios(unsigned long start_pfn, #ifdef CONFIG_MEMORY_FAILURE extern void folio_clear_hugetlb_hwpoison(struct folio *folio); +extern bool hugetlb_should_keep_hwpoison_mapped(struct folio *folio, + struct address_space *mapping); #else static inline void folio_clear_hugetlb_hwpoison(struct folio *folio) { } +static inline bool hugetlb_should_keep_hwpoison_mapped(struct folio *folio + struct address_space *mapping) +{ + return false; +} #endif #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 09b581c1d878d..9ad511aacde7c 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -213,6 +213,8 @@ enum mapping_flags { AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM = 9, AS_KERNEL_FILE = 10, /* mapping for a fake kernel file that shouldn't account usage to user cgroups */ + /* For MFD_MF_KEEP_UE_MAPPED. */ + AS_MF_KEEP_UE_MAPPED = 11, /* Bits 16-25 are used for FOLIO_ORDER */ AS_FOLIO_ORDER_BITS = 5, AS_FOLIO_ORDER_MIN = 16, @@ -348,6 +350,16 @@ static inline bool mapping_writeback_may_deadlock_on_reclaim(const struct addres return test_bit(AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM, &mapping->flags); } +static inline bool mapping_mf_keep_ue_mapped(const struct address_space *mapping) +{ + return test_bit(AS_MF_KEEP_UE_MAPPED, &mapping->flags); +} + +static inline void mapping_set_mf_keep_ue_mapped(struct address_space *mapping) +{ + set_bit(AS_MF_KEEP_UE_MAPPED, &mapping->flags); +} + static inline gfp_t mapping_gfp_mask(const struct address_space *mapping) { return mapping->gfp_mask; @@ -1274,6 +1286,18 @@ void replace_page_cache_folio(struct folio *old, struct folio *new); void delete_from_page_cache_batch(struct address_space *mapping, struct folio_batch *fbatch); bool filemap_release_folio(struct folio *folio, gfp_t gfp); +#ifdef CONFIG_MEMORY_FAILURE +/* + * Provided by memory failure to offline HWPoison-ed folio managed by memfd. + */ +void filemap_offline_hwpoison_folio(struct address_space *mapping, + struct folio *folio); +#else +void filemap_offline_hwpoison_folio(struct address_space *mapping, + struct folio *folio) +{ +} +#endif loff_t mapping_seek_hole_data(struct address_space *, loff_t start, loff_t end, int whence); diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h index 273a4e15dfcff..d9875da551b7f 100644 --- a/include/uapi/linux/memfd.h +++ b/include/uapi/linux/memfd.h @@ -12,6 +12,12 @@ #define MFD_NOEXEC_SEAL 0x0008U /* executable */ #define MFD_EXEC 0x0010U +/* + * Keep owned folios mapped when uncorrectable memory errors (UE) causes + * memory failure (MF) within the folio. Only at the end of the mapping + * will its HWPoison-ed folios be dealt with. + */ +#define MFD_MF_KEEP_UE_MAPPED 0x0020U /* * Huge page size encoding when MFD_HUGETLB is specified, and a huge page diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 0455119716ec0..dd3bc0b75e059 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6415,6 +6415,18 @@ static bool hugetlb_pte_stable(struct hstate *h, struct mm_struct *mm, unsigned return same; } +bool hugetlb_should_keep_hwpoison_mapped(struct folio *folio, + struct address_space *mapping) +{ + if (WARN_ON_ONCE(!folio_test_hugetlb(folio))) + return false; + + if (!mapping) + return false; + + return mapping_mf_keep_ue_mapped(mapping); +} + static vm_fault_t hugetlb_no_page(struct address_space *mapping, struct vm_fault *vmf) { @@ -6537,9 +6549,11 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping, * So we need to block hugepage fault by PG_hwpoison bit check. */ if (unlikely(folio_test_hwpoison(folio))) { - ret = VM_FAULT_HWPOISON_LARGE | - VM_FAULT_SET_HINDEX(hstate_index(h)); - goto backout_unlocked; + if (!mapping_mf_keep_ue_mapped(mapping)) { + ret = VM_FAULT_HWPOISON_LARGE | + VM_FAULT_SET_HINDEX(hstate_index(h)); + goto backout_unlocked; + } } /* Check for page in userfault range. */ diff --git a/mm/memfd.c b/mm/memfd.c index 1d109c1acf211..bfdde4cf90500 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -313,7 +313,8 @@ long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg) #define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1) #define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN) -#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | MFD_NOEXEC_SEAL | MFD_EXEC) +#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | \ + MFD_NOEXEC_SEAL | MFD_EXEC | MFD_MF_KEEP_UE_MAPPED) static int check_sysctl_memfd_noexec(unsigned int *flags) { @@ -387,6 +388,8 @@ static int sanitize_flags(unsigned int *flags_ptr) if (!(flags & MFD_HUGETLB)) { if (flags & ~MFD_ALL_FLAGS) return -EINVAL; + if (flags & MFD_MF_KEEP_UE_MAPPED) + return -EINVAL; } else { /* Allow huge page size encoding in flags. */ if (flags & ~(MFD_ALL_FLAGS | @@ -447,6 +450,16 @@ static struct file *alloc_file(const char *name, unsigned int flags) file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE; file->f_flags |= O_LARGEFILE; + /* + * MFD_MF_KEEP_UE_MAPPED can only be specified in memfd_create; no API + * to update it once memfd is created. MFD_MF_KEEP_UE_MAPPED is not + * seal-able. + * + * For now MFD_MF_KEEP_UE_MAPPED is only supported by HugeTLBFS. + */ + if (flags & (MFD_HUGETLB | MFD_MF_KEEP_UE_MAPPED)) + mapping_set_mf_keep_ue_mapped(file->f_mapping); + if (flags & MFD_NOEXEC_SEAL) { struct inode *inode = file_inode(file); diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 3edebb0cda30b..c5e3e28872797 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -373,11 +373,13 @@ static unsigned long dev_pagemap_mapping_shift(struct vm_area_struct *vma, * Schedule a process for later kill. * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM. */ -static void __add_to_kill(struct task_struct *tsk, const struct page *p, +static void __add_to_kill(struct task_struct *tsk, struct page *p, struct vm_area_struct *vma, struct list_head *to_kill, unsigned long addr) { struct to_kill *tk; + struct folio *folio; + struct address_space *mapping; tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC); if (!tk) { @@ -388,8 +390,19 @@ static void __add_to_kill(struct task_struct *tsk, const struct page *p, tk->addr = addr; if (is_zone_device_page(p)) tk->size_shift = dev_pagemap_mapping_shift(vma, tk->addr); - else - tk->size_shift = folio_shift(page_folio(p)); + else { + folio = page_folio(p); + mapping = folio_mapping(folio); + if (mapping && mapping_mf_keep_ue_mapped(mapping)) + /* + * Let userspace know the radius of HWPoison is + * the size of raw page; accessing other pages + * inside the folio is still ok. + */ + tk->size_shift = PAGE_SHIFT; + else + tk->size_shift = folio_shift(folio); + } /* * Send SIGKILL if "tk->addr == -EFAULT". Also, as @@ -414,7 +427,7 @@ static void __add_to_kill(struct task_struct *tsk, const struct page *p, list_add_tail(&tk->nd, to_kill); } -static void add_to_kill_anon_file(struct task_struct *tsk, const struct page *p, +static void add_to_kill_anon_file(struct task_struct *tsk, struct page *p, struct vm_area_struct *vma, struct list_head *to_kill, unsigned long addr) { @@ -535,7 +548,7 @@ struct task_struct *task_early_kill(struct task_struct *tsk, int force_early) * Collect processes when the error hit an anonymous page. */ static void collect_procs_anon(const struct folio *folio, - const struct page *page, struct list_head *to_kill, + struct page *page, struct list_head *to_kill, int force_early) { struct task_struct *tsk; @@ -573,7 +586,7 @@ static void collect_procs_anon(const struct folio *folio, * Collect processes when the error hit a file mapped page. */ static void collect_procs_file(const struct folio *folio, - const struct page *page, struct list_head *to_kill, + struct page *page, struct list_head *to_kill, int force_early) { struct vm_area_struct *vma; @@ -655,7 +668,7 @@ static void collect_procs_fsdax(const struct page *page, /* * Collect the processes who have the corrupted page mapped to kill. */ -static void collect_procs(const struct folio *folio, const struct page *page, +static void collect_procs(const struct folio *folio, struct page *page, struct list_head *tokill, int force_early) { if (!folio->mapping) @@ -1173,6 +1186,13 @@ static int me_huge_page(struct page_state *ps, struct page *p) } } + /* + * MF still needs to holds a refcount for the deferred actions in + * filemap_offline_hwpoison_folio. + */ + if (hugetlb_should_keep_hwpoison_mapped(folio, mapping)) + return res; + if (has_extra_refcount(ps, p, extra_pins)) res = MF_FAILED; @@ -1569,6 +1589,7 @@ static bool hwpoison_user_mappings(struct folio *folio, struct page *p, { LIST_HEAD(tokill); bool unmap_success; + bool keep_mapped; int forcekill; bool mlocked = folio_test_mlocked(folio); @@ -1596,8 +1617,12 @@ static bool hwpoison_user_mappings(struct folio *folio, struct page *p, */ collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED); - unmap_success = !unmap_poisoned_folio(folio, pfn, flags & MF_MUST_KILL); - if (!unmap_success) + keep_mapped = hugetlb_should_keep_hwpoison_mapped(folio, folio->mapping); + if (!keep_mapped) + unmap_poisoned_folio(folio, pfn, flags & MF_MUST_KILL); + + unmap_success = !folio_mapped(folio); + if (!keep_mapped && !unmap_success) pr_err("%#lx: failed to unmap page (folio mapcount=%d)\n", pfn, folio_mapcount(folio)); @@ -1622,7 +1647,7 @@ static bool hwpoison_user_mappings(struct folio *folio, struct page *p, !unmap_success; kill_procs(&tokill, forcekill, pfn, flags); - return unmap_success; + return unmap_success || keep_mapped; } static int identify_page_state(unsigned long pfn, struct page *p, @@ -1862,6 +1887,13 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag) unsigned long count = 0; head = llist_del_all(raw_hwp_list_head(folio)); + /* + * If filemap_offline_hwpoison_folio_hugetlb is handling this folio, + * it has already taken off the head of the llist. + */ + if (head == NULL) + return 0; + llist_for_each_entry_safe(p, next, head, node) { if (move_flag) SetPageHWPoison(p->page); @@ -1878,7 +1910,8 @@ static int folio_set_hugetlb_hwpoison(struct folio *folio, struct page *page) struct llist_head *head; struct raw_hwp_page *raw_hwp; struct raw_hwp_page *p; - int ret = folio_test_set_hwpoison(folio) ? -EHWPOISON : 0; + struct address_space *mapping = folio->mapping; + bool has_hwpoison = folio_test_set_hwpoison(folio); /* * Once the hwpoison hugepage has lost reliable raw error info, @@ -1897,8 +1930,15 @@ static int folio_set_hugetlb_hwpoison(struct folio *folio, struct page *page) if (raw_hwp) { raw_hwp->page = page; llist_add(&raw_hwp->node, head); + if (hugetlb_should_keep_hwpoison_mapped(folio, mapping)) + /* + * A new raw HWPoison page. Don't return HWPOISON. + * Error event will be counted in action_result(). + */ + return 0; + /* the first error event will be counted in action_result(). */ - if (ret) + if (has_hwpoison) num_poisoned_pages_inc(page_to_pfn(page)); } else { /* @@ -1913,7 +1953,8 @@ static int folio_set_hugetlb_hwpoison(struct folio *folio, struct page *page) */ __folio_free_raw_hwp(folio, false); } - return ret; + + return has_hwpoison ? -EHWPOISON : 0; } static unsigned long folio_free_raw_hwp(struct folio *folio, bool move_flag) @@ -2002,6 +2043,63 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags, return ret; } +static void filemap_offline_hwpoison_folio_hugetlb(struct folio *folio) +{ + int ret; + struct llist_node *head; + struct raw_hwp_page *curr, *next; + struct page *page; + unsigned long pfn; + + /* + * Since folio is still in the folio_batch, drop the refcount + * elevated by filemap_get_folios. + */ + folio_put_refs(folio, 1); + head = llist_del_all(raw_hwp_list_head(folio)); + + /* + * Release refcounts held by try_memory_failure_hugetlb, one per + * HWPoison-ed page in the raw hwp list. + */ + llist_for_each_entry(curr, head, node) { + SetPageHWPoison(curr->page); + folio_put(folio); + } + + /* Refcount now should be zero and ready to dissolve folio. */ + ret = dissolve_free_hugetlb_folio(folio); + if (ret) { + pr_err("failed to dissolve hugetlb folio: %d\n", ret); + return; + } + + llist_for_each_entry_safe(curr, next, head, node) { + page = curr->page; + pfn = page_to_pfn(page); + drain_all_pages(page_zone(page)); + if (!take_page_off_buddy(page)) + pr_err("%#lx: unable to take off buddy allocator\n", pfn); + + page_ref_inc(page); + kfree(curr); + pr_info("%#lx: pending hard offline completed\n", pfn); + } +} + +void filemap_offline_hwpoison_folio(struct address_space *mapping, + struct folio *folio) +{ + WARN_ON_ONCE(!mapping); + + if (!folio_test_hwpoison(folio)) + return; + + /* Pending MFR currently only exist for hugetlb. */ + if (hugetlb_should_keep_hwpoison_mapped(folio, mapping)) + filemap_offline_hwpoison_folio_hugetlb(folio); +} + /* * Taking refcount of hugetlb pages needs extra care about race conditions * with basic operations like hugepage allocation/free/demotion. -- 2.52.0.rc1.455.g30608eb744-goog Test the userspace memory failure recovery (MFR) policy for HugeTLB 1G or 2M hugepage case: 1. Create a memfd backed by HugeTLB and had MFD_MF_KEEP_UE_MAPPED set. 2. Allocate and map 4 hugepages to the process. 3. Create sub-threads to MADV_HWPOISON inner addresses of one hugepage. 4. Check if the process gets correct SIGBUS for each poisoned raw page. 5. Check if all memory are still accessible and content valid. 6. Check if the poisoned hugepage is dealt with after memfd released. Signed-off-by: Jiaqi Yan --- tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 1 + tools/testing/selftests/mm/hugetlb-mfr.c | 327 +++++++++++++++++++++++ 3 files changed, 329 insertions(+) create mode 100644 tools/testing/selftests/mm/hugetlb-mfr.c diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore index c2a8586e51a1f..11664d20935db 100644 --- a/tools/testing/selftests/mm/.gitignore +++ b/tools/testing/selftests/mm/.gitignore @@ -5,6 +5,7 @@ hugepage-mremap hugepage-shm hugepage-vmemmap hugetlb-madvise +hugetlb-mfr hugetlb-read-hwpoison hugetlb-soft-offline khugepaged diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index eaf9312097f7b..de3bdcf7914cd 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -63,6 +63,7 @@ TEST_GEN_FILES += hmm-tests TEST_GEN_FILES += hugetlb-madvise TEST_GEN_FILES += hugetlb-read-hwpoison TEST_GEN_FILES += hugetlb-soft-offline +TEST_GEN_FILES += hugetlb-mfr TEST_GEN_FILES += hugepage-mmap TEST_GEN_FILES += hugepage-mremap TEST_GEN_FILES += hugepage-shm diff --git a/tools/testing/selftests/mm/hugetlb-mfr.c b/tools/testing/selftests/mm/hugetlb-mfr.c new file mode 100644 index 0000000000000..30939b2194188 --- /dev/null +++ b/tools/testing/selftests/mm/hugetlb-mfr.c @@ -0,0 +1,327 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Test the userspace memory failure recovery (MFR) policy for HugeTLB + * hugepage case: + * 1. Create a memfd backed by HugeTLB and MFD_MF_KEEP_UE_MAPPED bit set. + * 2. Allocate and map 4 hugepages. + * 3. Create sub-threads to MADV_HWPOISON inner addresses of one hugepage. + * 4. Check if each sub-thread get correct SIGBUS for the poisoned raw page. + * 5. Check if all memory are still accessible and content still valid. + * 6. Check if the poisoned hugepage is dealt with after memfd released. + * + * Two ways to run the test: + * ./hugetlb-mfr 2M + * or + * ./hugetlb-mfr 1G + * assuming /sys/kernel/mm/hugepages/hugepages-${xxx}kB/nr_hugepages > 4 + */ + +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include +#include +#include +#include +#include +#include + +#include "../kselftest.h" +#include "vm_util.h" + +#define EPREFIX " !!! " +#define BYTE_LENTH_IN_1G 0x40000000UL +#define BYTE_LENTH_IN_2M 0x200000UL +#define HUGETLB_1GB_STR "1G" +#define HUGETLB_2MB_STR "2M" +#define HUGETLB_FILL 0xab + +static const unsigned long offsets_1g[] = {0x200000, 0x400000, 0x800000}; +static const unsigned long offsets_2m[] = {0x020000, 0x040000, 0x080000}; + +static void *sigbus_addr; +static int sigbus_addr_lsb; +static bool expecting_sigbus; +static bool got_sigbus; +static bool was_mceerr; + +static int create_hugetlbfs_file(struct statfs *file_stat, + unsigned long hugepage_size) +{ + int fd; + int flags = MFD_HUGETLB | MFD_MF_KEEP_UE_MAPPED; + + if (hugepage_size == BYTE_LENTH_IN_2M) + flags |= MFD_HUGE_2MB; + else + flags |= MFD_HUGE_1GB; + + fd = memfd_create("hugetlb_tmp", flags); + if (fd < 0) + ksft_exit_fail_perror("Failed to memfd_create"); + + memset(file_stat, 0, sizeof(*file_stat)); + if (fstatfs(fd, file_stat)) { + close(fd); + ksft_exit_fail_perror("Failed to fstatfs"); + } + if (file_stat->f_type != HUGETLBFS_MAGIC) { + close(fd); + ksft_exit_fail_msg("Not hugetlbfs file"); + } + + ksft_print_msg("Created hugetlb_tmp file\n"); + ksft_print_msg("hugepagesize=%#lx\n", file_stat->f_bsize); + if (file_stat->f_bsize != hugepage_size) + ksft_exit_fail_msg("Hugepage size is not %#lx", hugepage_size); + + return fd; +} + +/* + * SIGBUS handler for "do_hwpoison" thread that mapped and MADV_HWPOISON + */ +static void sigbus_handler(int signo, siginfo_t *info, void *context) +{ + if (!expecting_sigbus) + ksft_exit_fail_msg("unexpected sigbus with addr=%p", + info->si_addr); + + got_sigbus = true; + was_mceerr = (info->si_code == BUS_MCEERR_AO || + info->si_code == BUS_MCEERR_AR); + sigbus_addr = info->si_addr; + sigbus_addr_lsb = info->si_addr_lsb; +} + +static void *do_hwpoison(void *hwpoison_addr) +{ + int hwpoison_size = getpagesize(); + + ksft_print_msg("MADV_HWPOISON hwpoison_addr=%p, len=%d\n", + hwpoison_addr, hwpoison_size); + if (madvise(hwpoison_addr, hwpoison_size, MADV_HWPOISON) < 0) + ksft_exit_fail_perror("Failed to MADV_HWPOISON"); + + pthread_exit(NULL); +} + +static void test_hwpoison_multiple_pages(unsigned char *start_addr, + unsigned long hugepage_size) +{ + pthread_t pthread; + int ret; + unsigned char *hwpoison_addr; + const unsigned long *offsets; + size_t offsets_count; + size_t i; + + if (hugepage_size == BYTE_LENTH_IN_2M) { + offsets = offsets_2m; + offsets_count = ARRAY_SIZE(offsets_2m); + } else { + offsets = offsets_1g; + offsets_count = ARRAY_SIZE(offsets_1g); + } + + for (i = 0; i < offsets_count; ++i) { + sigbus_addr = (void *)0xBADBADBAD; + sigbus_addr_lsb = 0; + was_mceerr = false; + got_sigbus = false; + expecting_sigbus = true; + hwpoison_addr = start_addr + offsets[i]; + + ret = pthread_create(&pthread, NULL, &do_hwpoison, hwpoison_addr); + if (ret) + ksft_exit_fail_perror("Failed to create hwpoison thread"); + + ksft_print_msg("Created thread to hwpoison and access hwpoison_addr=%p\n", + hwpoison_addr); + + pthread_join(pthread, NULL); + + if (!got_sigbus) + ksft_test_result_fail("Didn't get a SIGBUS\n"); + if (!was_mceerr) + ksft_test_result_fail("Didn't get a BUS_MCEERR_A(R|O)\n"); + if (sigbus_addr != hwpoison_addr) + ksft_test_result_fail("Incorrect address: got=%p, expected=%p\n", + sigbus_addr, hwpoison_addr); + if (sigbus_addr_lsb != pshift()) + ksft_test_result_fail("Incorrect address LSB: got=%d, expected=%d\n", + sigbus_addr_lsb, pshift()); + + ksft_print_msg("Received expected and correct SIGBUS\n"); + } +} + +static int read_nr_hugepages(unsigned long hugepage_size, + unsigned long *nr_hugepages) +{ + char buffer[256] = {0}; + char cmd[256] = {0}; + + sprintf(cmd, "cat /sys/kernel/mm/hugepages/hugepages-%ldkB/nr_hugepages", + hugepage_size); + FILE *cmdfile = popen(cmd, "r"); + + if (cmdfile == NULL) { + ksft_perror(EPREFIX "failed to popen nr_hugepages"); + return -1; + } + + if (!fgets(buffer, sizeof(buffer), cmdfile)) { + ksft_perror(EPREFIX "failed to read nr_hugepages"); + pclose(cmdfile); + return -1; + } + + *nr_hugepages = atoll(buffer); + pclose(cmdfile); + return 0; +} + +/* + * Main thread that drives the test. + */ +static void test_main(int fd, unsigned long hugepage_size) +{ + unsigned char *map, *iter; + struct sigaction new, old; + const unsigned long hugepagesize_kb = hugepage_size / 1024; + unsigned long nr_hugepages_before = 0; + unsigned long nr_hugepages_after = 0; + unsigned long nodemask = 1UL << 0; + unsigned long len = hugepage_size * 4; + int ret; + + if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_before) != 0) { + close(fd); + ksft_exit_fail_msg("Failed to read nr_hugepages\n"); + } + ksft_print_msg("NR hugepages before MADV_HWPOISON is %ld\n", nr_hugepages_before); + + if (ftruncate(fd, len) < 0) + ksft_exit_fail_perror("Failed to ftruncate"); + + ksft_print_msg("Allocated %#lx bytes to HugeTLB file\n", len); + + map = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + if (map == MAP_FAILED) + ksft_exit_fail_msg("Failed to mmap"); + + ksft_print_msg("Created HugeTLB mapping: %p\n", map); + + ret = mbind(map, len, MPOL_BIND, &nodemask, sizeof(nodemask) * 8, + MPOL_MF_STRICT | MPOL_MF_MOVE); + if (ret < 0) { + perror("mbind"); + ksft_exit_fail_msg("Failed to bind to node\n"); + } + + memset(map, HUGETLB_FILL, len); + ksft_print_msg("Memset every byte to 0xab\n"); + + new.sa_sigaction = &sigbus_handler; + new.sa_flags = SA_SIGINFO; + if (sigaction(SIGBUS, &new, &old) < 0) + ksft_exit_fail_msg("Failed to setup SIGBUS handler"); + + ksft_print_msg("Setup SIGBUS handler successfully\n"); + + test_hwpoison_multiple_pages(map, hugepage_size); + + /* + * Since MADV_HWPOISON doesn't corrupt the memory in hardware, and + * MFD_MF_KEEP_UE_MAPPED keeps the hugepage mapped, every byte should + * remain accessible and hold original data. + */ + expecting_sigbus = false; + for (iter = map; iter < map + len; ++iter) { + if (*iter != HUGETLB_FILL) { + ksft_print_msg("At addr=%p: got=%#x, expected=%#x\n", + iter, *iter, HUGETLB_FILL); + ksft_test_result_fail("Memory content corrupted\n"); + break; + } + } + ksft_print_msg("Memory content all valid\n"); + + if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_after) != 0) { + close(fd); + ksft_exit_fail_msg("Failed to read nr_hugepages\n"); + } + + /* + * After MADV_HWPOISON, hugepage should still be in HugeTLB pool. + */ + ksft_print_msg("NR hugepages after MADV_HWPOISON is %ld\n", nr_hugepages_after); + if (nr_hugepages_before != nr_hugepages_after) + ksft_test_result_fail("NR hugepages reduced by %ld after MADV_HWPOISON\n", + nr_hugepages_before - nr_hugepages_after); + + /* End of the lifetime of the created HugeTLB memfd. */ + if (ftruncate(fd, 0) < 0) + ksft_exit_fail_perror("Failed to ftruncate to 0"); + munmap(map, len); + close(fd); + + /* + * After freed by userspace, MADV_HWPOISON-ed hugepage should be + * dissolved into raw pages and removed from HugeTLB pool. + */ + if (read_nr_hugepages(hugepagesize_kb, &nr_hugepages_after) != 0) { + close(fd); + ksft_exit_fail_msg("Failed to read nr_hugepages\n"); + } + ksft_print_msg("NR hugepages after closure is %ld\n", nr_hugepages_after); + if (nr_hugepages_before != nr_hugepages_after + 1) + ksft_test_result_fail("NR hugepages is not reduced after memfd closure\n"); + + ksft_test_result_pass("All done\n"); +} + +static unsigned long parse_hugepage_size(char *argv) +{ + if (strncasecmp(argv, HUGETLB_1GB_STR, strlen(HUGETLB_1GB_STR)) == 0) + return BYTE_LENTH_IN_1G; + + if (strncasecmp(argv, HUGETLB_2MB_STR, strlen(HUGETLB_2MB_STR)) == 0) + return BYTE_LENTH_IN_2M; + + ksft_print_msg("Please provide valid hugepage_size: 1G or 2M\n"); + assert(false); +} + +int main(int argc, char **argv) +{ + int fd; + struct statfs file_stat; + unsigned long hugepage_size; + + if (argc != 2) { + ksft_print_msg("Usage: %s \n", argv[0]); + return -EINVAL; + } + + ksft_print_header(); + ksft_set_plan(1); + + hugepage_size = parse_hugepage_size(argv[1]); + fd = create_hugetlbfs_file(&file_stat, hugepage_size); + test_main(fd, hugepage_size); + + ksft_finished(); +} -- 2.52.0.rc1.455.g30608eb744-goog Document its motivation, userspace API, behaviors, and limitations. Signed-off-by: Jiaqi Yan --- Documentation/userspace-api/index.rst | 1 + .../userspace-api/mfd_mfr_policy.rst | 60 +++++++++++++++++++ 2 files changed, 61 insertions(+) create mode 100644 Documentation/userspace-api/mfd_mfr_policy.rst diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index b8c73be4fb112..d8c6977d9e67a 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -67,6 +67,7 @@ Everything else futex2 perf_ring_buffer ntsync + mfd_mfr_policy .. only:: subproject and html diff --git a/Documentation/userspace-api/mfd_mfr_policy.rst b/Documentation/userspace-api/mfd_mfr_policy.rst new file mode 100644 index 0000000000000..c5a25df39791a --- /dev/null +++ b/Documentation/userspace-api/mfd_mfr_policy.rst @@ -0,0 +1,60 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================================== +Userspace Memory Failure Recovery Policy via memfd +================================================== + +:Author: + Jiaqi Yan + + +Motivation +========== + +When a userspace process is able to recover from memory failures (MF) +caused by uncorrected memory error (UE) in the DIMM, especially when it is +able to avoid consuming known UEs, keeping the memory page mapped and +accessible is benifical to the owning process for a couple of reasons: + +- The memory pages affected by UE have a large smallest granularity, for + example 1G hugepage, but the actual corrupted amount of the page is only + several cachlines. Losing the entire hugepage of data is unacceptable to + the application. + +- In addition to keeping the data accessible, the application still wants + to access with a large page size for the fastest virtual-to-physical + translations. + +Memory failure recovery for 1G or larger HugeTLB is a good example. With +memfd userspace process can control whether the kernel hard offlines its +hugepages that backs the in-RAM file created by memfd. + + +User API +======== + +``int memfd_create(const char *name, unsigned int flags)`` + +``MFD_MF_KEEP_UE_MAPPED`` + + When ``MFD_MF_KEEP_UE_MAPPED`` bit is set in ``flags``, MF recovery + in the kernel does not hard offline memory due to UE until the + returned ``memfd`` is released. IOW, the HWPoison-ed memory remains + accessible via the returned ``memfd`` or the memory mapping created + with the returned ``memfd``. Note the affected memory will be + immediately isolated and prevented from future use once the memfd + is closed. By default ``MFD_MF_KEEP_UE_MAPPED`` is not set, and + kernel hard offlines memory having UEs. + +Notes about the behavior and limitations + +- Even if the page affected by UE is kept, a portion of the (huge)page is + already lost due to hardware corruption, and the size of the portion + is the smallest page size that kernel uses to manages memory on the + architecture, i.e. PAGESIZE. Accessing a virtual address within any of + these parts results in a SIGBUS; accessing virtual address outside these + parts are good until it is corrupted by new memory error. + +- ``MFD_MF_KEEP_UE_MAPPED`` currently only works for HugeTLB, so + ``MFD_HUGETLB`` must also be set when setting ``MFD_MF_KEEP_UE_MAPPED``. + Otherwise ``memfd_create`` returns EINVAL. -- 2.52.0.rc1.455.g30608eb744-goog