[PATCH v2 24/46] hugetlb: add HGM support to hugetlb_fault and hugetlb_no_page
From: James Houghton
Date: Fri Feb 17 2023 - 19:30:29 EST
Update the page fault handler to support high-granularity page faults.
While handling a page fault on a partially-mapped HugeTLB page, if the
PTE we find with hugetlb_pte_walk is none, then we will replace it with
a leaf-level PTE to map the page. To give some examples:
1. For a completely unmapped 1G page, it will be mapped with a 1G PUD.
2. For a 1G page that has its first 512M mapped, any faults on the
unmapped sections will result in 2M PMDs mapping each unmapped 2M
section.
3. For a 1G page that has only its first 4K mapped, a page fault on its
second 4K section will get a 4K PTE to map it.
Unless high-granularity mappings are created via UFFDIO_CONTINUE, it is
impossible for hugetlb_fault to create high-granularity mappings.
This commit does not handle hugetlb_wp right now, and it doesn't handle
HugeTLB page migration and swap entries.
The BUG_ON in huge_pte_alloc is removed, as it is not longer valid when
HGM is possible. HGM can be disabled if the VMA lock cannot be allocated
after a VMA is split, yet high-granularity mappings may still exist.
Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6c4678b7a07d..86cd51beb02c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -173,6 +173,18 @@ void hugetlb_add_file_rmap(struct page *subpage, unsigned long shift,
}
}
+/*
+ * Find the subpage that corresponds to `addr` in `folio`.
+ */
+static struct page *hugetlb_find_subpage(struct hstate *h, struct folio *folio,
+ unsigned long addr)
+{
+ size_t idx = (addr & ~huge_page_mask(h))/PAGE_SIZE;
+
+ BUG_ON(idx >= pages_per_huge_page(h));
+ return folio_page(folio, idx);
+}
+
static inline bool subpool_is_free(struct hugepage_subpool *spool)
{
if (spool->count)
@@ -6072,14 +6084,14 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma,
* Recheck pte with pgtable lock. Returns true if pte didn't change, or
* false if pte changed or is changing.
*/
-static bool hugetlb_pte_stable(struct hstate *h, struct mm_struct *mm,
- pte_t *ptep, pte_t old_pte)
+static bool hugetlb_pte_stable(struct hstate *h, struct hugetlb_pte *hpte,
+ pte_t old_pte)
{
spinlock_t *ptl;
bool same;
- ptl = huge_pte_lock(h, mm, ptep);
- same = pte_same(huge_ptep_get(ptep), old_pte);
+ ptl = hugetlb_pte_lock(hpte);
+ same = pte_same(huge_ptep_get(hpte->ptep), old_pte);
spin_unlock(ptl);
return same;
@@ -6088,7 +6100,7 @@ static bool hugetlb_pte_stable(struct hstate *h, struct mm_struct *mm,
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);
@@ -6096,10 +6108,12 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
int anon_rmap = 0;
unsigned long size;
struct folio *folio;
+ struct page *subpage;
pte_t new_pte;
spinlock_t *ptl;
unsigned long haddr = address & huge_page_mask(h);
bool new_folio, new_pagecache_folio = false;
+ unsigned long haddr_hgm = address & hugetlb_pte_mask(hpte);
u32 hash = hugetlb_fault_mutex_hash(mapping, idx);
/*
@@ -6143,7 +6157,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
* never happen on the page after UFFDIO_COPY has
* correctly installed the page and returned.
*/
- if (!hugetlb_pte_stable(h, mm, ptep, old_pte)) {
+ if (!hugetlb_pte_stable(h, hpte, old_pte)) {
ret = 0;
goto out;
}
@@ -6167,7 +6181,7 @@ 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.
*/
- if (hugetlb_pte_stable(h, mm, ptep, old_pte))
+ if (hugetlb_pte_stable(h, hpte, old_pte))
ret = vmf_error(PTR_ERR(folio));
else
ret = 0;
@@ -6217,7 +6231,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
folio_unlock(folio);
folio_put(folio);
/* See comment in userfaultfd_missing() block above */
- if (!hugetlb_pte_stable(h, mm, ptep, old_pte)) {
+ if (!hugetlb_pte_stable(h, hpte, old_pte)) {
ret = 0;
goto out;
}
@@ -6242,30 +6256,46 @@ 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(hpte);
ret = 0;
- /* If pte changed from under us, retry */
- if (!pte_same(huge_ptep_get(ptep), old_pte))
+ /*
+ * If pte changed from under us, retry.
+ *
+ * When dealing with high-granularity-mapped PTEs, it's possible that
+ * a non-contiguous PTE within our contiguous PTE group gets populated,
+ * in which case, we need to retry here. This is NOT caught here, and
+ * will need to be addressed when HGM is supported for architectures
+ * that support contiguous PTEs.
+ */
+ if (!pte_same(huge_ptep_get(hpte->ptep), old_pte))
goto backout;
- if (anon_rmap)
+ subpage = hugetlb_find_subpage(h, folio, haddr_hgm);
+
+ if (anon_rmap) {
+ VM_BUG_ON(&folio->page != subpage);
hugepage_add_new_anon_rmap(folio, vma, haddr);
+ }
else
- page_add_file_rmap(&folio->page, vma, true);
- new_pte = make_huge_pte(vma, &folio->page, ((vma->vm_flags & VM_WRITE)
- && (vma->vm_flags & VM_SHARED)));
+ hugetlb_add_file_rmap(subpage, hpte->shift, h, vma);
+
+ new_pte = make_huge_pte_with_shift(vma, subpage,
+ ((vma->vm_flags & VM_WRITE)
+ && (vma->vm_flags & VM_SHARED)),
+ hpte->shift);
/*
* If this pte was previously wr-protected, keep it wr-protected even
* if populated.
*/
if (unlikely(pte_marker_uffd_wp(old_pte)))
new_pte = 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)) {
+ WARN_ON_ONCE(hugetlb_pte_size(hpte) != huge_page_size(h));
/* Optimization, do the COW without a second fault */
- ret = hugetlb_wp(mm, vma, address, ptep, flags, folio, ptl);
+ ret = hugetlb_wp(mm, vma, address, hpte->ptep, flags, folio, ptl);
}
spin_unlock(ptl);
@@ -6322,17 +6352,19 @@ u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx)
vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, unsigned int flags)
{
- pte_t *ptep, entry;
+ pte_t entry;
spinlock_t *ptl;
vm_fault_t ret;
u32 hash;
pgoff_t idx;
- struct page *page = NULL;
- struct folio *pagecache_folio = NULL;
+ struct page *subpage = NULL;
+ struct folio *pagecache_folio = NULL, *folio = 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;
+ struct hugetlb_pte hpte;
/*
* Serialize hugepage allocation and instantiation, so that we don't
@@ -6346,26 +6378,26 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
/*
* Acquire vma lock before calling huge_pte_alloc and hold
- * until finished with ptep. This prevents huge_pmd_unshare from
- * being called elsewhere and making the ptep no longer valid.
+ * until finished with hpte. This prevents huge_pmd_unshare from
+ * being called elsewhere and making the hpte no longer valid.
*/
hugetlb_vma_lock_read(vma);
- ptep = huge_pte_alloc(mm, vma, haddr, huge_page_size(h));
- if (!ptep) {
+ if (hugetlb_full_walk_alloc(&hpte, vma, address, 0)) {
hugetlb_vma_unlock_read(vma);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
return VM_FAULT_OOM;
}
- entry = huge_ptep_get(ptep);
+ entry = huge_ptep_get(hpte.ptep);
/* PTE markers should be handled the same way as none pte */
- if (huge_pte_none_mostly(entry))
+ if (huge_pte_none_mostly(entry)) {
/*
* hugetlb_no_page will drop vma lock and hugetlb fault
* mutex internally, which make us return immediately.
*/
- return hugetlb_no_page(mm, vma, mapping, idx, address, ptep,
+ return hugetlb_no_page(mm, vma, mapping, idx, address, &hpte,
entry, flags);
+ }
ret = 0;
@@ -6386,7 +6418,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* be released there.
*/
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
- migration_entry_wait_huge(vma, ptep);
+ migration_entry_wait_huge(vma, hpte.ptep);
return 0;
} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
ret = VM_FAULT_HWPOISON_LARGE |
@@ -6394,6 +6426,10 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
goto out_mutex;
}
+ if (!hugetlb_pte_present_leaf(&hpte, entry))
+ /* We raced with someone splitting the entry. */
+ goto out_mutex;
+
/*
* If we are going to COW/unshare the mapping later, we examine the
* pending reservations for this page now. This will ensure that any
@@ -6413,14 +6449,17 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
pagecache_folio = filemap_lock_folio(mapping, idx);
}
- ptl = huge_pte_lock(h, mm, ptep);
+ ptl = hugetlb_pte_lock(&hpte);
/* Check for a racing update before calling hugetlb_wp() */
- if (unlikely(!pte_same(entry, huge_ptep_get(ptep))))
+ if (unlikely(!pte_same(entry, huge_ptep_get(hpte.ptep))))
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(entry) &&
(flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
struct vm_fault vmf = {
.vma = vma,
@@ -6444,18 +6483,21 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* pagecache_folio, so here we need take the former one
* when page != pagecache_folio or !pagecache_folio.
*/
- page = pte_page(entry);
- if (page_folio(page) != pagecache_folio)
- if (!trylock_page(page)) {
+ subpage = pte_page(entry);
+ folio = page_folio(subpage);
+ if (folio != pagecache_folio)
+ if (!trylock_page(&folio->page)) {
need_wait_lock = 1;
goto out_ptl;
}
- get_page(page);
+ folio_get(folio);
if (flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) {
if (!huge_pte_write(entry)) {
- ret = hugetlb_wp(mm, vma, address, ptep, flags,
+ WARN_ON_ONCE(hugetlb_pte_size(&hpte) !=
+ huge_page_size(h));
+ ret = hugetlb_wp(mm, vma, address, hpte.ptep, flags,
pagecache_folio, ptl);
goto out_put_page;
} else if (likely(flags & FAULT_FLAG_WRITE)) {
@@ -6463,13 +6505,13 @@ 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_folio(page) != pagecache_folio)
- unlock_page(page);
- put_page(page);
+ if (folio != pagecache_folio)
+ folio_unlock(folio);
+ folio_put(folio);
out_ptl:
spin_unlock(ptl);
@@ -6488,7 +6530,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* here without taking refcount.
*/
if (need_wait_lock)
- wait_on_page_locked(page);
+ wait_on_page_locked(&folio->page);
return ret;
}
@@ -7689,6 +7731,9 @@ int hugetlb_full_walk(struct hugetlb_pte *hpte,
/*
* hugetlb_full_walk_alloc - do a high-granularity walk, potentially allocate
* new PTEs.
+ *
+ * If @target_sz is 0, then only attempt to allocate the hstate-level PTE and
+ * walk as far as we can go.
*/
int hugetlb_full_walk_alloc(struct hugetlb_pte *hpte,
struct vm_area_struct *vma,
@@ -7707,6 +7752,12 @@ int hugetlb_full_walk_alloc(struct hugetlb_pte *hpte,
if (!ptep)
return -ENOMEM;
+ if (!target_sz) {
+ WARN_ON_ONCE(hugetlb_hgm_walk(hpte, ptep, vma, addr,
+ PAGE_SIZE, false));
+ return 0;
+ }
+
return hugetlb_hgm_walk(hpte, ptep, vma, addr, target_sz, true);
}
@@ -7735,7 +7786,6 @@ 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));
return pte;
}
--
2.39.2.637.g21b0678d19-goog