lkml.org 
[lkml]   [2023]   [Jan]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[PATCH] hugetlb: unshare some PMDs when splitting VMAs
From
PMD sharing can only be done in PUD_SIZE-aligned pieces of VMAs;
however, it is possible that HugeTLB VMAs are split without unsharing
the PMDs first.

In some (most?) cases, this is a non-issue, like userfaultfd_register
and mprotect, where PMDs are unshared before anything is done. However,
mbind() and madvise() (like MADV_DONTDUMP) can cause a split without
unsharing first.

It might seem ideal to unshare in hugetlb_vm_op_open, but that would
only unshare PMDs in the new VMA.

Signed-off-by: James Houghton <jthoughton@google.com>
---
mm/hugetlb.c | 42 +++++++++++++++++++++++++++++++++---------
1 file changed, 33 insertions(+), 9 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b39b74e0591a..bf7a1f628357 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -94,6 +94,8 @@ static int hugetlb_acct_memory(struct hstate *h, long delta);
static void hugetlb_vma_lock_free(struct vm_area_struct *vma);
static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma);
static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma);
+static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end);

static inline bool subpool_is_free(struct hugepage_subpool *spool)
{
@@ -4828,6 +4830,23 @@ static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
{
if (addr & ~(huge_page_mask(hstate_vma(vma))))
return -EINVAL;
+
+ /* We require PUD_SIZE VMA alignment for PMD sharing. */
+ if (addr & ~PUD_MASK) {
+ /*
+ * hugetlb_vm_op_split is called right before we attempt to
+ * split the VMA. We will need to unshare PMDs in the old and
+ * new VMAs, so let's unshare before we split.
+ */
+ unsigned long floor = addr & PUD_MASK;
+ unsigned long ceil = floor + PUD_SIZE;
+
+ if (floor < vma->vm_start || ceil >= vma->vm_end)
+ /* PMD sharing is already impossible. */
+ return 0;
+ hugetlb_unshare_pmds(vma, floor, ceil);
+ }
+
return 0;
}

@@ -7313,26 +7332,21 @@ void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, int re
}
}

-/*
- * This function will unconditionally remove all the shared pmd pgtable entries
- * within the specific vma for a hugetlbfs memory range.
- */
-void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
+static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
+ unsigned long start,
+ unsigned long end)
{
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
struct mm_struct *mm = vma->vm_mm;
struct mmu_notifier_range range;
- unsigned long address, start, end;
+ unsigned long address;
spinlock_t *ptl;
pte_t *ptep;

if (!(vma->vm_flags & VM_MAYSHARE))
return;

- start = ALIGN(vma->vm_start, PUD_SIZE);
- end = ALIGN_DOWN(vma->vm_end, PUD_SIZE);
-
if (start >= end)
return;

@@ -7364,6 +7378,16 @@ void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
mmu_notifier_invalidate_range_end(&range);
}

+/*
+ * This function will unconditionally remove all the shared pmd pgtable entries
+ * within the specific vma for a hugetlbfs memory range.
+ */
+void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
+{
+ hugetlb_unshare_pmds(vma, ALIGN(vma->vm_start, PUD_SIZE),
+ ALIGN_DOWN(vma->vm_end, PUD_SIZE));
+}
+
#ifdef CONFIG_CMA
static bool cma_reserve_called __initdata;

--
2.39.0.314.g84b9a713c41-goog
\
 
 \ /
  Last update: 2023-03-26 23:24    [W:0.172 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site