Messages in this thread | | | Date | Wed, 29 Jun 2022 20:10:16 +0530 | Subject | Re: [RFC PATCH 14/26] hugetlb: add HGM support for hugetlb_fault and hugetlb_no_page | From | "manish.mishra" <> |
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On 24/06/22 11:06 pm, James Houghton wrote: > This CL is the first main functional HugeTLB change. Together, these > changes allow the HugeTLB fault path to handle faults on HGM-enabled > VMAs. The two main behaviors that can be done now: > 1. Faults can be passed to handle_userfault. (Userspace will want to > use UFFD_FEATURE_REAL_ADDRESS to get the real address to know which > region they should be call UFFDIO_CONTINUE on later.) > 2. Faults on pages that have been partially mapped (and userfaultfd is > not being used) will get mapped at the largest possible size. > For example, if a 1G page has been partially mapped at 2M, and we > fault on an unmapped 2M section, hugetlb_no_page will create a 2M > PMD to map the faulting address. > > This commit does not handle hugetlb_wp right now, and it doesn't handle > HugeTLB page migration and swap entries. > > Signed-off-by: James Houghton <jthoughton@google.com> > --- > include/linux/hugetlb.h | 12 ++++ > mm/hugetlb.c | 121 +++++++++++++++++++++++++++++++--------- > 2 files changed, 106 insertions(+), 27 deletions(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 321f5745d87f..ac4ac8fbd901 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -1185,6 +1185,9 @@ enum split_mode { > #ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING > /* If HugeTLB high-granularity mappings are enabled for this VMA. */ > bool hugetlb_hgm_enabled(struct vm_area_struct *vma); > +int hugetlb_alloc_largest_pte(struct hugetlb_pte *hpte, struct mm_struct *mm, > + struct vm_area_struct *vma, unsigned long start, > + unsigned long end); > int huge_pte_alloc_high_granularity(struct hugetlb_pte *hpte, > struct mm_struct *mm, > struct vm_area_struct *vma, > @@ -1197,6 +1200,15 @@ static inline bool hugetlb_hgm_enabled(struct vm_area_struct *vma) > { > return false; > } > + > +static inline > +int hugetlb_alloc_largest_pte(struct hugetlb_pte *hpte, struct mm_struct *mm, > + struct vm_area_struct *vma, unsigned long start, > + unsigned long end) > +{ > + BUG(); > +} > + > static inline int huge_pte_alloc_high_granularity(struct hugetlb_pte *hpte, > struct mm_struct *mm, > struct vm_area_struct *vma, > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 6e0c5fbfe32c..da30621656b8 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5605,18 +5605,24 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma, > static vm_fault_t hugetlb_no_page(struct mm_struct *mm, > struct vm_area_struct *vma, > struct address_space *mapping, pgoff_t idx, > - unsigned long address, pte_t *ptep, > + unsigned long address, struct hugetlb_pte *hpte, > pte_t old_pte, unsigned int flags) > { > struct hstate *h = hstate_vma(vma); > vm_fault_t ret = VM_FAULT_SIGBUS; > int anon_rmap = 0; > unsigned long size; > - struct page *page; > + struct page *page, *subpage; > pte_t new_pte; > spinlock_t *ptl; > unsigned long haddr = address & huge_page_mask(h); > + unsigned long haddr_hgm = address & hugetlb_pte_mask(hpte); > bool new_page, new_pagecache_page = false; > + /* > + * This page is getting mapped for the first time, in which case we > + * want to increment its mapcount. > + */ > + bool new_mapping = hpte->shift == huge_page_shift(h); > > /* > * Currently, we are forced to kill the process in the event the > @@ -5665,9 +5671,9 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, > * here. Before returning error, get ptl and make > * sure there really is no pte entry. > */ > - ptl = huge_pte_lock(h, mm, ptep); > + ptl = hugetlb_pte_lock(mm, hpte); > ret = 0; > - if (huge_pte_none(huge_ptep_get(ptep))) > + if (hugetlb_pte_none(hpte)) > ret = vmf_error(PTR_ERR(page)); > spin_unlock(ptl); > goto out; > @@ -5731,18 +5737,25 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, > vma_end_reservation(h, vma, haddr); > } > > - ptl = huge_pte_lock(h, mm, ptep); > + ptl = hugetlb_pte_lock(mm, hpte); > ret = 0; > /* If pte changed from under us, retry */ > - if (!pte_same(huge_ptep_get(ptep), old_pte)) > + if (!pte_same(hugetlb_ptep_get(hpte), old_pte)) > goto backout; > > - if (anon_rmap) { > - ClearHPageRestoreReserve(page); > - hugepage_add_new_anon_rmap(page, vma, haddr); > - } else > - page_dup_file_rmap(page, true); > - new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE) > + if (new_mapping) { > + /* Only increment this page's mapcount if we are mapping it > + * for the first time. > + */ > + if (anon_rmap) { > + ClearHPageRestoreReserve(page); > + hugepage_add_new_anon_rmap(page, vma, haddr); > + } else > + page_dup_file_rmap(page, true); > + } > + > + subpage = hugetlb_find_subpage(h, page, haddr_hgm);
sorry did not understand why make_huge_pte we may be mapping just PAGE_SIZE
too here.
> + new_pte = make_huge_pte(vma, subpage, ((vma->vm_flags & VM_WRITE) > && (vma->vm_flags & VM_SHARED))); > /* > * If this pte was previously wr-protected, keep it wr-protected even > @@ -5750,12 +5763,13 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, > */ > if (unlikely(pte_marker_uffd_wp(old_pte))) > new_pte = huge_pte_wrprotect(huge_pte_mkuffd_wp(new_pte)); > - set_huge_pte_at(mm, haddr, ptep, new_pte); > + set_huge_pte_at(mm, haddr_hgm, hpte->ptep, new_pte); > > - hugetlb_count_add(pages_per_huge_page(h), mm); > + hugetlb_count_add(hugetlb_pte_size(hpte) / PAGE_SIZE, mm); > if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) { > + BUG_ON(hugetlb_pte_size(hpte) != huge_page_size(h)); > /* Optimization, do the COW without a second fault */ > - ret = hugetlb_wp(mm, vma, address, ptep, flags, page, ptl); > + ret = hugetlb_wp(mm, vma, address, hpte->ptep, flags, page, ptl); > } > > spin_unlock(ptl); > @@ -5816,11 +5830,15 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > u32 hash; > pgoff_t idx; > struct page *page = NULL; > + struct page *subpage = NULL; > struct page *pagecache_page = NULL; > struct hstate *h = hstate_vma(vma); > struct address_space *mapping; > int need_wait_lock = 0; > unsigned long haddr = address & huge_page_mask(h); > + unsigned long haddr_hgm; > + bool hgm_enabled = hugetlb_hgm_enabled(vma); > + struct hugetlb_pte hpte; > > ptep = huge_pte_offset(mm, haddr, huge_page_size(h)); > if (ptep) { > @@ -5866,11 +5884,22 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > hash = hugetlb_fault_mutex_hash(mapping, idx); > mutex_lock(&hugetlb_fault_mutex_table[hash]); > > - entry = huge_ptep_get(ptep); > + hugetlb_pte_populate(&hpte, ptep, huge_page_shift(h)); > + > + if (hgm_enabled) { > + ret = hugetlb_walk_to(mm, &hpte, address, > + PAGE_SIZE, /*stop_at_none=*/true); > + if (ret) { > + ret = vmf_error(ret); > + goto out_mutex; > + } > + } > + > + entry = hugetlb_ptep_get(&hpte); > /* PTE markers should be handled the same way as none pte */ > - if (huge_pte_none_mostly(entry)) { > - ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep, > - entry, flags); > + if (hugetlb_pte_none_mostly(&hpte)) { > + ret = hugetlb_no_page(mm, vma, mapping, idx, address, &hpte, > + entry, flags); > goto out_mutex; > } > > @@ -5908,14 +5937,17 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > vma, haddr); > } > > - ptl = huge_pte_lock(h, mm, ptep); > + ptl = hugetlb_pte_lock(mm, &hpte); > > /* Check for a racing update before calling hugetlb_wp() */ > - if (unlikely(!pte_same(entry, huge_ptep_get(ptep)))) > + if (unlikely(!pte_same(entry, hugetlb_ptep_get(&hpte)))) > goto out_ptl; > > + /* haddr_hgm is the base address of the region that hpte maps. */ > + haddr_hgm = address & hugetlb_pte_mask(&hpte); > + > /* Handle userfault-wp first, before trying to lock more pages */ > - if (userfaultfd_wp(vma) && huge_pte_uffd_wp(huge_ptep_get(ptep)) && > + if (userfaultfd_wp(vma) && huge_pte_uffd_wp(hugetlb_ptep_get(&hpte)) && > (flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) { > struct vm_fault vmf = { > .vma = vma, > @@ -5939,7 +5971,8 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > * pagecache_page, so here we need take the former one > * when page != pagecache_page or !pagecache_page. > */ > - page = pte_page(entry); > + subpage = pte_page(entry); > + page = compound_head(subpage); > if (page != pagecache_page) > if (!trylock_page(page)) { > need_wait_lock = 1; > @@ -5950,7 +5983,8 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > > if (flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) { > if (!huge_pte_write(entry)) { > - ret = hugetlb_wp(mm, vma, address, ptep, flags, > + BUG_ON(hugetlb_pte_size(&hpte) != huge_page_size(h));
is it in respect to fact that userfault_wp is not support with HGM mapping currently? Not
sure yet though how it is controlled may be next patches will have more details.
> + ret = hugetlb_wp(mm, vma, address, hpte.ptep, flags, > pagecache_page, ptl); > goto out_put_page; > } else if (likely(flags & FAULT_FLAG_WRITE)) { > @@ -5958,9 +5992,9 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > } > } > entry = pte_mkyoung(entry); > - if (huge_ptep_set_access_flags(vma, haddr, ptep, entry, > + if (huge_ptep_set_access_flags(vma, haddr_hgm, hpte.ptep, entry, > flags & FAULT_FLAG_WRITE)) > - update_mmu_cache(vma, haddr, ptep); > + update_mmu_cache(vma, haddr_hgm, hpte.ptep); > out_put_page: > if (page != pagecache_page) > unlock_page(page); > @@ -6951,7 +6985,8 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma, > pte = (pte_t *)pmd_alloc(mm, pud, addr); > } > } > - BUG_ON(pte && pte_present(*pte) && !pte_huge(*pte)); > + if (!hugetlb_hgm_enabled(vma)) > + BUG_ON(pte && pte_present(*pte) && !pte_huge(*pte)); > > return pte; > } > @@ -7057,6 +7092,38 @@ static unsigned int __shift_for_hstate(struct hstate *h) > (tmp_h) <= &hstates[hugetlb_max_hstate]; \ > (tmp_h)++) > > +/* > + * Allocate a HugeTLB PTE that maps as much of [start, end) as possible with a > + * single page table entry. The allocated HugeTLB PTE is returned in hpte. > + */
Will it be used for madvise_collapase? If so will it make sense to keep it in different patch
as this one title says just for handle_page_fault routines.
> +int hugetlb_alloc_largest_pte(struct hugetlb_pte *hpte, struct mm_struct *mm, > + struct vm_area_struct *vma, unsigned long start, > + unsigned long end) > +{ > + struct hstate *h = hstate_vma(vma), *tmp_h; > + unsigned int shift; > + int ret; > + > + for_each_hgm_shift(h, tmp_h, shift) { > + unsigned long sz = 1UL << shift; > + > + if (!IS_ALIGNED(start, sz) || start + sz > end) > + continue; > + ret = huge_pte_alloc_high_granularity(hpte, mm, vma, start, > + shift, HUGETLB_SPLIT_NONE, > + /*write_locked=*/false); > + if (ret) > + return ret; > + > + if (hpte->shift > shift) > + return -EEXIST; > + > + BUG_ON(hpte->shift != shift); > + return 0; > + } > + return -EINVAL; > +} > + > /* > * Given a particular address, split the HugeTLB PTE that currently maps it > * so that, for the given address, the PTE that maps it is `desired_shift`.
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