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SubjectRe: [RFC PATCH 14/26] hugetlb: add HGM support for hugetlb_fault and hugetlb_no_page
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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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