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.
Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
mm/hugetlb.c | 90 +++++++++++++++++++++++++++++++++++++---------------
1 file changed, 64 insertions(+), 26 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 16b0d192445c..2ee2c48ee79c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -118,6 +118,18 @@ enum hugetlb_level hpage_size_to_level(unsigned long sz)
return HUGETLB_LEVEL_PGD;
}
+/*
+ * Find the subpage that corresponds to `addr` in `hpage`.
+ */
+static struct page *hugetlb_find_subpage(struct hstate *h, struct page *hpage,
+ unsigned long addr)
+{
+ size_t idx = (addr & ~huge_page_mask(h))/PAGE_SIZE;
+
+ BUG_ON(idx >= pages_per_huge_page(h));
+ return &hpage[idx];
+}
+
static inline bool subpool_is_free(struct hugepage_subpool *spool)
{
if (spool->count)
@@ -5810,13 +5822,13 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma,
* 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)
+ 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(mm, hpte);
+ same = pte_same(huge_ptep_get(hpte->ptep), old_pte);
spin_unlock(ptl);
return same;
@@ -5825,17 +5837,18 @@ 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);
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;
u32 hash = hugetlb_fault_mutex_hash(mapping, idx);
@@ -5880,7 +5893,7 @@ 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, mm, hpte, old_pte)) {
ret = 0;
goto out;
}
@@ -5904,7 +5917,7 @@ 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, mm, hpte, old_pte))
ret = vmf_error(PTR_ERR(page));
else
ret = 0;
@@ -5954,7 +5967,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
unlock_page(page);
put_page(page);
/* See comment in userfaultfd_missing() block above */
- if (!hugetlb_pte_stable(h, mm, ptep, old_pte)) {
+ if (!hugetlb_pte_stable(h, mm, hpte, old_pte)) {
ret = 0;
goto out;
}
@@ -5979,10 +5992,10 @@ 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(huge_ptep_get(hpte->ptep), old_pte))
goto backout;
if (anon_rmap) {
@@ -5990,20 +6003,25 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
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)
- && (vma->vm_flags & VM_SHARED)));
+
+ subpage = hugetlb_find_subpage(h, page, haddr_hgm);
+ 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_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);
@@ -6066,11 +6084,14 @@ 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;
+ struct hugetlb_pte hpte;
ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
if (ptep) {
@@ -6115,15 +6136,22 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
return VM_FAULT_OOM;
}
- entry = huge_ptep_get(ptep);
+ hugetlb_pte_populate(&hpte, ptep, huge_page_shift(h),
+ hpage_size_to_level(huge_page_size(h)));
+ /* Do a high-granularity page table walk. */
+ hugetlb_hgm_walk(mm, vma, &hpte, address, PAGE_SIZE,
+ /*stop_at_none=*/true);
+
+ 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;
@@ -6137,6 +6165,10 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
if (!pte_present(entry))
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
@@ -6156,14 +6188,17 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
pagecache_page = find_lock_page(mapping, idx);
}
- 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, 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,
@@ -6187,7 +6222,8 @@ 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;
@@ -6198,7 +6234,8 @@ 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));
+ ret = hugetlb_wp(mm, vma, address, hpte.ptep, flags,
pagecache_page, ptl);
goto out_put_page;
} else if (likely(flags & FAULT_FLAG_WRITE)) {
@@ -6206,9 +6243,9 @@ 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);
@@ -7598,7 +7635,8 @@ 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));
+ BUG_ON(pte && pte_present(*pte) && !pte_huge(*pte) &&
+ !hugetlb_hgm_enabled(vma));
return pte;
}
--
2.38.0.135.g90850a2211-goog
