[PATCH 4.14 072/106] hugetlb: take PMD sharing into account when flushing tlb/caches

Greg Kroah-Hartman
2021-12-06T15:13:44Z

From: Mike Kravetz <mike.kravetz@oracle.com>

commit dff11abe280b47c21b804a8ace318e0638bb9a49 upstream.

When fixing an issue with PMD sharing and migration, it was discovered via
code inspection that other callers of huge_pmd_unshare potentially have an
issue with cache and tlb flushing.

Use the routine adjust_range_if_pmd_sharing_possible() to calculate worst
case ranges for mmu notifiers. Ensure that this range is flushed if
huge_pmd_unshare succeeds and unmaps a PUD_SUZE area.

Link: http://lkml.kernel.org/r/20180823205917.16297-3-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/hugetlb.c | 53 +++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 43 insertions(+), 10 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3384,8 +3384,8 @@ void __unmap_hugepage_range(struct mmu_g
struct page *page;
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
- const unsigned long mmun_start = start; /* For mmu_notifiers */
- const unsigned long mmun_end = end; /* For mmu_notifiers */
+ unsigned long mmun_start = start; /* For mmu_notifiers */
+ unsigned long mmun_end = end; /* For mmu_notifiers */
bool force_flush = false;

WARN_ON(!is_vm_hugetlb_page(vma));
@@ -3398,6 +3398,11 @@ void __unmap_hugepage_range(struct mmu_g
*/
tlb_remove_check_page_size_change(tlb, sz);
tlb_start_vma(tlb, vma);
+
+ /*
+ * If sharing possible, alert mmu notifiers of worst case.
+ */
+ adjust_range_if_pmd_sharing_possible(vma, &mmun_start, &mmun_end);
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
address = start;
for (; address < end; address += sz) {
@@ -3508,12 +3513,23 @@ void unmap_hugepage_range(struct vm_area
{
struct mm_struct *mm;
struct mmu_gather tlb;
+ unsigned long tlb_start = start;
+ unsigned long tlb_end = end;
+
+ /*
+ * If shared PMDs were possibly used within this vma range, adjust
+ * start/end for worst case tlb flushing.
+ * Note that we can not be sure if PMDs are shared until we try to
+ * unmap pages. However, we want to make sure TLB flushing covers
+ * the largest possible range.
+ */
+ adjust_range_if_pmd_sharing_possible(vma, &tlb_start, &tlb_end);

mm = vma->vm_mm;

- tlb_gather_mmu(&tlb, mm, start, end);
+ tlb_gather_mmu(&tlb, mm, tlb_start, tlb_end);
__unmap_hugepage_range(&tlb, vma, start, end, ref_page);
- tlb_finish_mmu(&tlb, start, end);
+ tlb_finish_mmu(&tlb, tlb_start, tlb_end);
}

/*
@@ -4408,11 +4424,21 @@ unsigned long hugetlb_change_protection(
pte_t pte;
struct hstate *h = hstate_vma(vma);
unsigned long pages = 0;
+ unsigned long f_start = start;
+ unsigned long f_end = end;
+ bool shared_pmd = false;
+
+ /*
+ * In the case of shared PMDs, the area to flush could be beyond
+ * start/end. Set f_start/f_end to cover the maximum possible
+ * range if PMD sharing is possible.
+ */
+ adjust_range_if_pmd_sharing_possible(vma, &f_start, &f_end);

BUG_ON(address >= end);
- flush_cache_range(vma, address, end);
+ flush_cache_range(vma, f_start, f_end);

- mmu_notifier_invalidate_range_start(mm, start, end);
+ mmu_notifier_invalidate_range_start(mm, f_start, f_end);
i_mmap_lock_write(vma->vm_file->f_mapping);
for (; address < end; address += huge_page_size(h)) {
spinlock_t *ptl;
@@ -4423,6 +4449,7 @@ unsigned long hugetlb_change_protection(
if (huge_pmd_unshare(mm, &address, ptep)) {
pages++;
spin_unlock(ptl);
+ shared_pmd = true;
continue;
}
pte = huge_ptep_get(ptep);
@@ -4458,12 +4485,18 @@ unsigned long hugetlb_change_protection(
* Must flush TLB before releasing i_mmap_rwsem: x86's huge_pmd_unshare
* may have cleared our pud entry and done put_page on the page table:
* once we release i_mmap_rwsem, another task can do the final put_page
- * and that page table be reused and filled with junk.
+ * and that page table be reused and filled with junk. If we actually
+ * did unshare a page of pmds, flush the range corresponding to the pud.
*/
- flush_hugetlb_tlb_range(vma, start, end);
- mmu_notifier_invalidate_range(mm, start, end);
+ if (shared_pmd) {
+ flush_hugetlb_tlb_range(vma, f_start, f_end);
+ mmu_notifier_invalidate_range(mm, f_start, f_end);
+ } else {
+ flush_hugetlb_tlb_range(vma, start, end);
+ mmu_notifier_invalidate_range(mm, start, end);
+ }
i_mmap_unlock_write(vma->vm_file->f_mapping);
- mmu_notifier_invalidate_range_end(mm, start, end);
+ mmu_notifier_invalidate_range_end(mm, f_start, f_end);

return pages << h->order;
}