summaryrefslogtreecommitdiff
path: root/mm/huge_memory.c
diff options
context:
space:
mode:
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c125
1 files changed, 86 insertions, 39 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 530e6427f823..b2d56b1c3276 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -135,8 +135,7 @@ static void set_recommended_min_free_kbytes(void)
if (recommended_min > min_free_kbytes) {
if (user_min_free_kbytes >= 0)
- pr_info("raising min_free_kbytes from %d to %lu "
- "to help transparent hugepage allocations\n",
+ pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
min_free_kbytes, recommended_min);
min_free_kbytes = recommended_min;
@@ -1269,6 +1268,16 @@ out_unlock:
return ret;
}
+/*
+ * FOLL_FORCE can write to even unwritable pmd's, but only
+ * after we've gone through a COW cycle and they are dirty.
+ */
+static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
+{
+ return pmd_write(pmd) ||
+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
+}
+
struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
unsigned long addr,
pmd_t *pmd,
@@ -1279,7 +1288,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
assert_spin_locked(pmd_lockptr(mm, pmd));
- if (flags & FOLL_WRITE && !pmd_write(*pmd))
+ if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
goto out;
/* Avoid dumping huge zero page */
@@ -1294,17 +1303,11 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
VM_BUG_ON_PAGE(!PageHead(page), page);
if (flags & FOLL_TOUCH) {
pmd_t _pmd;
- /*
- * We should set the dirty bit only for FOLL_WRITE but
- * for now the dirty bit in the pmd is meaningless.
- * And if the dirty bit will become meaningful and
- * we'll only set it with FOLL_WRITE, an atomic
- * set_bit will be required on the pmd to set the
- * young bit, instead of the current set_pmd_at.
- */
- _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
+ _pmd = pmd_mkyoung(*pmd);
+ if (flags & FOLL_WRITE)
+ _pmd = pmd_mkdirty(_pmd);
if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
- pmd, _pmd, 1))
+ pmd, _pmd, flags & FOLL_WRITE))
update_mmu_cache_pmd(vma, addr, pmd);
}
if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
@@ -1353,8 +1356,11 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
*/
if (unlikely(pmd_trans_migrating(*pmdp))) {
page = pmd_page(*pmdp);
+ if (!get_page_unless_zero(page))
+ goto out_unlock;
spin_unlock(ptl);
wait_on_page_locked(page);
+ put_page(page);
goto out;
}
@@ -1386,9 +1392,12 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
/* Migration could have started since the pmd_trans_migrating check */
if (!page_locked) {
+ page_nid = -1;
+ if (!get_page_unless_zero(page))
+ goto out_unlock;
spin_unlock(ptl);
wait_on_page_locked(page);
- page_nid = -1;
+ put_page(page);
goto out;
}
@@ -1501,7 +1510,7 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
spinlock_t *old_ptl, *new_ptl;
int ret = 0;
pmd_t pmd;
-
+ bool force_flush = false;
struct mm_struct *mm = vma->vm_mm;
if ((old_addr & ~HPAGE_PMD_MASK) ||
@@ -1529,6 +1538,8 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
if (new_ptl != old_ptl)
spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
+ if (pmd_present(pmd))
+ force_flush = true;
VM_BUG_ON(!pmd_none(*new_pmd));
if (pmd_move_must_withdraw(new_ptl, old_ptl)) {
@@ -1537,6 +1548,8 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
}
set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
+ if (force_flush)
+ flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
if (new_ptl != old_ptl)
spin_unlock(new_ptl);
spin_unlock(old_ptl);
@@ -1556,35 +1569,69 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
{
struct mm_struct *mm = vma->vm_mm;
spinlock_t *ptl;
+ pmd_t entry;
+ bool preserve_write;
+
int ret = 0;
- if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
- pmd_t entry;
- bool preserve_write = prot_numa && pmd_write(*pmd);
- ret = 1;
+ if (__pmd_trans_huge_lock(pmd, vma, &ptl) != 1)
+ return 0;
- /*
- * Avoid trapping faults against the zero page. The read-only
- * data is likely to be read-cached on the local CPU and
- * local/remote hits to the zero page are not interesting.
- */
- if (prot_numa && is_huge_zero_pmd(*pmd)) {
- spin_unlock(ptl);
- return ret;
- }
+ preserve_write = prot_numa && pmd_write(*pmd);
+ ret = 1;
- if (!prot_numa || !pmd_protnone(*pmd)) {
- entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
- entry = pmd_modify(entry, newprot);
- if (preserve_write)
- entry = pmd_mkwrite(entry);
- ret = HPAGE_PMD_NR;
- set_pmd_at(mm, addr, pmd, entry);
- BUG_ON(!preserve_write && pmd_write(entry));
- }
- spin_unlock(ptl);
- }
+ /*
+ * Avoid trapping faults against the zero page. The read-only
+ * data is likely to be read-cached on the local CPU and
+ * local/remote hits to the zero page are not interesting.
+ */
+ if (prot_numa && is_huge_zero_pmd(*pmd))
+ goto unlock;
+ if (prot_numa && pmd_protnone(*pmd))
+ goto unlock;
+
+ /*
+ * In case prot_numa, we are under down_read(mmap_sem). It's critical
+ * to not clear pmd intermittently to avoid race with MADV_DONTNEED
+ * which is also under down_read(mmap_sem):
+ *
+ * CPU0: CPU1:
+ * change_huge_pmd(prot_numa=1)
+ * pmdp_huge_get_and_clear_notify()
+ * madvise_dontneed()
+ * zap_pmd_range()
+ * pmd_trans_huge(*pmd) == 0 (without ptl)
+ * // skip the pmd
+ * set_pmd_at();
+ * // pmd is re-established
+ *
+ * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
+ * which may break userspace.
+ *
+ * pmdp_invalidate() is required to make sure we don't miss
+ * dirty/young flags set by hardware.
+ */
+ entry = *pmd;
+ pmdp_invalidate(vma, addr, pmd);
+
+ /*
+ * Recover dirty/young flags. It relies on pmdp_invalidate to not
+ * corrupt them.
+ */
+ if (pmd_dirty(*pmd))
+ entry = pmd_mkdirty(entry);
+ if (pmd_young(*pmd))
+ entry = pmd_mkyoung(entry);
+
+ entry = pmd_modify(entry, newprot);
+ if (preserve_write)
+ entry = pmd_mkwrite(entry);
+ ret = HPAGE_PMD_NR;
+ set_pmd_at(mm, addr, pmd, entry);
+ BUG_ON(!preserve_write && pmd_write(entry));
+unlock:
+ spin_unlock(ptl);
return ret;
}
generated by cgit v1.2.3 (git 2.25.1) at 2025-12-10 17:44:05 +0000