On 24/06/22 11:06 pm, James Houghton wrote:
This enables support for GUP, and it is needed for the KVM demand paging
self-test to work.
One important change here is that, before, we never needed to grab the
i_mmap_sem, but now, to prevent someone from collapsing the page tables
out from under us, we grab it for reading when doing high-granularity PT
walks.
Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
mm/hugetlb.c | 70 ++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 57 insertions(+), 13 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f9c7daa6c090..aadfcee947cf 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6298,14 +6298,18 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long vaddr = *position;
unsigned long remainder = *nr_pages;
struct hstate *h = hstate_vma(vma);
+ struct address_space *mapping = vma->vm_file->f_mapping;
int err = -EFAULT, refs;
+ bool has_i_mmap_sem = false;
while (vaddr < vma->vm_end && remainder) {
pte_t *pte;
spinlock_t *ptl = NULL;
bool unshare = false;
int absent;
+ unsigned long pages_per_hpte;
struct page *page;
+ struct hugetlb_pte hpte;
/*
* If we have a pending SIGKILL, don't keep faulting pages and
@@ -6325,9 +6329,23 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
*/
pte = huge_pte_offset(mm, vaddr & huge_page_mask(h),
huge_page_size(h));
- if (pte)
- ptl = huge_pte_lock(h, mm, pte);
- absent = !pte || huge_pte_none(huge_ptep_get(pte));
+ if (pte) {
+ hugetlb_pte_populate(&hpte, pte, huge_page_shift(h));
+ if (hugetlb_hgm_enabled(vma)) {
+ BUG_ON(has_i_mmap_sem);
Just thinking can we do without i_mmap_lock_read in most cases. Like earlier
this function was good without i_mmap_lock_read doing almost everything
which is happening now?
+ i_mmap_lock_read(mapping);
+ /*
+ * Need to hold the mapping semaphore for
+ * reading to do a HGM walk.
+ */
+ has_i_mmap_sem = true;
+ hugetlb_walk_to(mm, &hpte, vaddr, PAGE_SIZE,
+ /*stop_at_none=*/true);
+ }
+ ptl = hugetlb_pte_lock(mm, &hpte);
+ }
+
+ absent = !pte || hugetlb_pte_none(&hpte);
/*
* When coredumping, it suits get_dump_page if we just return
@@ -6338,8 +6356,13 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
*/
if (absent && (flags & FOLL_DUMP) &&
!hugetlbfs_pagecache_present(h, vma, vaddr)) {
- if (pte)
+ if (pte) {
+ if (has_i_mmap_sem) {
+ i_mmap_unlock_read(mapping);
+ has_i_mmap_sem = false;
+ }
spin_unlock(ptl);
+ }
remainder = 0;
break;
}
@@ -6359,8 +6382,13 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
vm_fault_t ret;
unsigned int fault_flags = 0;
- if (pte)
+ if (pte) {
+ if (has_i_mmap_sem) {
+ i_mmap_unlock_read(mapping);
+ has_i_mmap_sem = false;
+ }
spin_unlock(ptl);
+ }
if (flags & FOLL_WRITE)
fault_flags |= FAULT_FLAG_WRITE;
else if (unshare)
@@ -6403,8 +6431,11 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
continue;
}
- pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
- page = pte_page(huge_ptep_get(pte));
+ pfn_offset = (vaddr & ~hugetlb_pte_mask(&hpte)) >> PAGE_SHIFT;
+ page = pte_page(hugetlb_ptep_get(&hpte));
+ pages_per_hpte = hugetlb_pte_size(&hpte) / PAGE_SIZE;
+ if (hugetlb_hgm_enabled(vma))
+ page = compound_head(page);
VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
!PageAnonExclusive(page), page);
@@ -6414,17 +6445,21 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
* and skip the same_page loop below.
*/
if (!pages && !vmas && !pfn_offset &&
- (vaddr + huge_page_size(h) < vma->vm_end) &&
- (remainder >= pages_per_huge_page(h))) {
- vaddr += huge_page_size(h);
- remainder -= pages_per_huge_page(h);
- i += pages_per_huge_page(h);
+ (vaddr + pages_per_hpte < vma->vm_end) &&
+ (remainder >= pages_per_hpte)) {
+ vaddr += pages_per_hpte;
+ remainder -= pages_per_hpte;
+ i += pages_per_hpte;
spin_unlock(ptl);
+ if (has_i_mmap_sem) {
+ has_i_mmap_sem = false;
+ i_mmap_unlock_read(mapping);
+ }
continue;
}
/* vaddr may not be aligned to PAGE_SIZE */
- refs = min3(pages_per_huge_page(h) - pfn_offset, remainder,
+ refs = min3(pages_per_hpte - pfn_offset, remainder,
(vma->vm_end - ALIGN_DOWN(vaddr, PAGE_SIZE)) >> PAGE_SHIFT);
if (pages || vmas)
@@ -6447,6 +6482,10 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
if (WARN_ON_ONCE(!try_grab_folio(pages[i], refs,
flags))) {
spin_unlock(ptl);
+ if (has_i_mmap_sem) {
+ has_i_mmap_sem = false;
+ i_mmap_unlock_read(mapping);
+ }
remainder = 0;
err = -ENOMEM;
break;
@@ -6458,8 +6497,13 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
i += refs;
spin_unlock(ptl);
+ if (has_i_mmap_sem) {
+ has_i_mmap_sem = false;
+ i_mmap_unlock_read(mapping);
+ }
}
*nr_pages = remainder;
+ BUG_ON(has_i_mmap_sem);
/*
* setting position is actually required only if remainder is
* not zero but it's faster not to add a "if (remainder)"
Thanks
Manish Mishra
