On Mon, Dec 05, 2022 at 03:40:58PM -0800, Jiaqi Yan wrote:
> Make __collapse_huge_page_copy return whether copying anonymous pages
> succeeded, and make collapse_huge_page handle the return status.
>
> Break existing PTE scan loop into two for-loops. The first loop copies
> source pages into target huge page, and can fail gracefully when running
> into memory errors in source pages. If copying all pages succeeds, the
> second loop releases and clears up these normal pages. Otherwise, the
> second loop rolls back the page table and page states by:
> - re-establishing the original PTEs-to-PMD connection.
> - releasing source pages back to their LRU list.
>
> Tested manually:
> 0. Enable khugepaged on system under test.
> 1. Start a two-thread application. Each thread allocates a chunk of
> non-huge anonymous memory buffer.
> 2. Pick 4 random buffer locations (2 in each thread) and inject
> uncorrectable memory errors at corresponding physical addresses.
> 3. Signal both threads to make their memory buffer collapsible, i.e.
> calling madvise(MADV_HUGEPAGE).
> 4. Wait and check kernel log: khugepaged is able to recover from poisoned
> pages and skips collapsing them.
> 5. Signal both threads to inspect their buffer contents and make sure no
> data corruption.
>
> Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
> ---
> include/trace/events/huge_memory.h | 3 +-
> mm/khugepaged.c | 179 ++++++++++++++++++++++-------
> 2 files changed, 139 insertions(+), 43 deletions(-)
>
> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
> index 35d759d3b0104..5743ae970af31 100644
> --- a/include/trace/events/huge_memory.h
> +++ b/include/trace/events/huge_memory.h
> @@ -36,7 +36,8 @@
> EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \
> EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \
> EM( SCAN_TRUNCATED, "truncated") \
> - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
> + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
> + EMe(SCAN_COPY_MC, "copy_poisoned_page") \
>
> #undef EM
> #undef EMe
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 5a7d2d5093f9c..0f1b9e05e17ec 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -19,6 +19,7 @@
> #include <linux/page_table_check.h>
> #include <linux/swapops.h>
> #include <linux/shmem_fs.h>
> +#include <linux/kmsan.h>
>
> #include <asm/tlb.h>
> #include <asm/pgalloc.h>
> @@ -55,6 +56,7 @@ enum scan_result {
> SCAN_CGROUP_CHARGE_FAIL,
> SCAN_TRUNCATED,
> SCAN_PAGE_HAS_PRIVATE,
> + SCAN_COPY_MC,
> };
>
> #define CREATE_TRACE_POINTS
> @@ -530,6 +532,27 @@ static bool is_refcount_suitable(struct page *page)
> return page_count(page) == expected_refcount;
> }
>
> +/*
> + * Copies memory with #MC in source page (@from) handled. Returns number
> + * of bytes not copied if there was an exception; otherwise 0 for success.
> + * Note handling #MC requires arch opt-in.
> + */
> +static int copy_mc_page(struct page *to, struct page *from)
> +{
> + char *vfrom, *vto;
> + unsigned long ret;
> +
> + vfrom = kmap_local_page(from);
> + vto = kmap_local_page(to);
> + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE);
> + if (ret == 0)
> + kmsan_copy_page_meta(to, from);
> + kunmap_local(vto);
> + kunmap_local(vfrom);
> +
> + return ret;
> +}
It is very similar to copy_mc_user_highpage(), but uses
kmsan_copy_page_meta() instead of kmsan_unpoison_memory().
Could you explain the difference? I don't quite get it.
> +
> static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> unsigned long address,
> pte_t *pte,
> @@ -670,56 +693,124 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> return result;
> }
>
> -static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
> - struct vm_area_struct *vma,
> - unsigned long address,
> - spinlock_t *ptl,
> - struct list_head *compound_pagelist)
> +/*
> + * __collapse_huge_page_copy - attempts to copy memory contents from normal
> + * pages to a hugepage. Cleans up the normal pages if copying succeeds;
> + * otherwise restores the original page table and releases isolated normal pages.
> + * Returns SCAN_SUCCEED if copying succeeds, otherwise returns SCAN_COPY_MC.
> + *
> + * @pte: starting of the PTEs to copy from
> + * @page: the new hugepage to copy contents to
> + * @pmd: pointer to the new hugepage's PMD
> + * @rollback: the original normal pages' PMD
> + * @vma: the original normal pages' virtual memory area
> + * @address: starting address to copy
> + * @pte_ptl: lock on normal pages' PTEs
> + * @compound_pagelist: list that stores compound pages
> + */
> +static int __collapse_huge_page_copy(pte_t *pte,
> + struct page *page,
> + pmd_t *pmd,
> + pmd_t rollback,
I think 'orig_pmd' is a better name.
> + struct vm_area_struct *vma,
> + unsigned long address,
> + spinlock_t *pte_ptl,
> + struct list_head *compound_pagelist)
> {
> struct page *src_page, *tmp;
> pte_t *_pte;
> - for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
> - _pte++, page++, address += PAGE_SIZE) {
> - pte_t pteval = *_pte;
> + pte_t pteval;
> + unsigned long _address;
> + spinlock_t *pmd_ptl;
> + int result = SCAN_SUCCEED;
>
> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> - clear_user_highpage(page, address);
> - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
> - if (is_zero_pfn(pte_pfn(pteval))) {
> + /*
> + * Copying pages' contents is subject to memory poison at any iteration.
> + */
> + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
> + _pte++, page++, _address += PAGE_SIZE) {
> + pteval = *_pte;
> +
> + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval)))
> + clear_user_highpage(page, _address);
> + else {
> + src_page = pte_page(pteval);
> + if (copy_mc_page(page, src_page) > 0) {
> + result = SCAN_COPY_MC;
> + break;
> + }
> + }
> + }
> +
> + if (likely(result == SCAN_SUCCEED)) {
> + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
> + _pte++, _address += PAGE_SIZE) {
> + pteval = *_pte;
> + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
> + if (is_zero_pfn(pte_pfn(pteval))) {
> + /*
> + * pte_ptl mostly unnecessary.
> + */
> + spin_lock(pte_ptl);
> + pte_clear(vma->vm_mm, _address, _pte);
> + spin_unlock(pte_ptl);
> + }
> + } else {
> + src_page = pte_page(pteval);
> + if (!PageCompound(src_page))
> + release_pte_page(src_page);
> /*
> - * ptl mostly unnecessary.
> + * pte_ptl mostly unnecessary, but preempt has
> + * to be disabled to update the per-cpu stats
> + * inside page_remove_rmap().
> */
> - spin_lock(ptl);
> - ptep_clear(vma->vm_mm, address, _pte);
> - spin_unlock(ptl);
> + spin_lock(pte_ptl);
> + ptep_clear(vma->vm_mm, _address, _pte);
> + page_remove_rmap(src_page, vma, false);
> + spin_unlock(pte_ptl);
> + free_page_and_swap_cache(src_page);
> + }
> + }
> + list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
> + list_del(&src_page->lru);
> + mod_node_page_state(page_pgdat(src_page),
> + NR_ISOLATED_ANON + page_is_file_lru(src_page),
> + -compound_nr(src_page));
> + unlock_page(src_page);
> + free_swap_cache(src_page);
> + putback_lru_page(src_page);
> + }
> + } else {
> + /*
> + * Re-establish the regular PMD that points to the regular
> + * page table. Restoring PMD needs to be done prior to
> + * releasing pages. Since pages are still isolated and
> + * locked here, acquiring anon_vma_lock_write is unnecessary.
> + */
> + pmd_ptl = pmd_lock(vma->vm_mm, pmd);
> + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback));
> + spin_unlock(pmd_ptl);
> + /*
> + * Release both raw and compound pages isolated
> + * in __collapse_huge_page_isolate.
> + */
> + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
> + _pte++, _address += PAGE_SIZE) {
> + pteval = *_pte;
> + if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval))) {
> + src_page = pte_page(pteval);
> + if (!PageCompound(src_page))
> + release_pte_page(src_page);
Indentation levels get out of control. Maybe some code restructuring is
required?
> }
> - } else {
> - src_page = pte_page(pteval);
> - copy_user_highpage(page, src_page, address, vma);
> - if (!PageCompound(src_page))
> - release_pte_page(src_page);
> - /*
> - * ptl mostly unnecessary, but preempt has to
> - * be disabled to update the per-cpu stats
> - * inside page_remove_rmap().
> - */
> - spin_lock(ptl);
> - ptep_clear(vma->vm_mm, address, _pte);
> - page_remove_rmap(src_page, vma, false);
> - spin_unlock(ptl);
> - free_page_and_swap_cache(src_page);
> + }
> + list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
> + list_del(&src_page->lru);
> + release_pte_page(src_page);
> }
> }
>
> - list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
> - list_del(&src_page->lru);
> - mod_node_page_state(page_pgdat(src_page),
> - NR_ISOLATED_ANON + page_is_file_lru(src_page),
> - -compound_nr(src_page));
> - unlock_page(src_page);
> - free_swap_cache(src_page);
> - putback_lru_page(src_page);
> - }
> + return result;
> }
>
> static void khugepaged_alloc_sleep(void)
> @@ -1079,9 +1170,13 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
> */
> anon_vma_unlock_write(vma->anon_vma);
>
> - __collapse_huge_page_copy(pte, hpage, vma, address, pte_ptl,
> - &compound_pagelist);
> + result = __collapse_huge_page_copy(pte, hpage, pmd, _pmd,
> + vma, address, pte_ptl,
> + &compound_pagelist);
> pte_unmap(pte);
> + if (unlikely(result != SCAN_SUCCEED))
> + goto out_up_write;
> +
> /*
> * spin_lock() below is not the equivalent of smp_wmb(), but
> * the smp_wmb() inside __SetPageUptodate() can be reused to
> --
> 2.39.0.rc0.267.gcb52ba06e7-goog
>
--
Kiryl Shutsemau / Kirill A. Shutemov
