These functions are used to allocate new PTEs below the hstate PTE. This
will be used by hugetlb_walk_step, which implements stepping forwards in
a HugeTLB high-granularity page table walk.
The reasons that we don't use the standard pmd_alloc/pte_alloc*
functions are:
1) This prevents us from accidentally overwriting swap entries or
attempting to use swap entries as present non-leaf PTEs (see
pmd_alloc(); we assume that !pte_none means pte_present and
non-leaf).
2) Locking hugetlb PTEs can different than regular PTEs. (Although, as
implemented right now, locking is the same.)
3) We can maintain compatibility with CONFIG_HIGHPTE. That is, HugeTLB
HGM won't use HIGHPTE, but the kernel can still be built with it,
and other mm code will use it.
When GENERAL_HUGETLB supports P4D-based hugepages, we will need to
implement hugetlb_pud_alloc to implement hugetlb_walk_step.
Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
include/linux/hugetlb.h | 5 ++
mm/hugetlb.c | 114 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 119 insertions(+)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index bf441d8a1b52..ad9d19f0d1b9 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -86,6 +86,11 @@ unsigned long hugetlb_pte_mask(const struct hugetlb_pte *hpte)
bool hugetlb_pte_present_leaf(const struct hugetlb_pte *hpte, pte_t pte);
+pmd_t *hugetlb_alloc_pmd(struct mm_struct *mm, struct hugetlb_pte *hpte,
+ unsigned long addr);
+pte_t *hugetlb_alloc_pte(struct mm_struct *mm, struct hugetlb_pte *hpte,
+ unsigned long addr);
+
struct hugepage_subpool {
spinlock_t lock;
long count;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2d83a2c359a2..2160cbaf3311 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -480,6 +480,120 @@ static bool has_same_uncharge_info(struct file_region *rg,
#endif
}
+/*
+ * hugetlb_alloc_pmd -- Allocate or find a PMD beneath a PUD-level hpte.
+ *
+ * This is meant to be used to implement hugetlb_walk_step when one must go to
+ * step down to a PMD. Different architectures may implement hugetlb_walk_step
+ * differently, but hugetlb_alloc_pmd and hugetlb_alloc_pte are architecture-
+ * independent.
+ *
+ * Returns:
+ * On success: the pointer to the PMD. This should be placed into a
+ * hugetlb_pte. @hpte is not changed.
+ * ERR_PTR(-EINVAL): hpte is not PUD-level
+ * ERR_PTR(-EEXIST): there is a non-leaf and non-empty PUD in @hpte
+ * ERR_PTR(-ENOMEM): could not allocate the new PMD
+ */
+pmd_t *hugetlb_alloc_pmd(struct mm_struct *mm, struct hugetlb_pte *hpte,
+ unsigned long addr)
+{
+ spinlock_t *ptl = hugetlb_pte_lockptr(hpte);
+ pmd_t *new;
+ pud_t *pudp;
+ pud_t pud;
+
+ if (hpte->level != HUGETLB_LEVEL_PUD)
+ return ERR_PTR(-EINVAL);
+
+ pudp = (pud_t *)hpte->ptep;
+retry:
+ pud = READ_ONCE(*pudp);
+ if (likely(pud_present(pud)))
+ return unlikely(pud_leaf(pud))
+ ? ERR_PTR(-EEXIST)
+ : pmd_offset(pudp, addr);
+ else if (!pud_none(pud))
+ /*
+ * Not present and not none means that a swap entry lives here,
+ * and we can't get rid of it.
+ */
+ return ERR_PTR(-EEXIST);
+
+ new = pmd_alloc_one(mm, addr);
+ if (!new)
+ return ERR_PTR(-ENOMEM);
+
+ spin_lock(ptl);
+ if (!pud_same(pud, *pudp)) {
+ spin_unlock(ptl);
+ pmd_free(mm, new);
+ goto retry;
+ }
+
+ mm_inc_nr_pmds(mm);
+ smp_wmb(); /* See comment in pmd_install() */
+ pud_populate(mm, pudp, new);
+ spin_unlock(ptl);
+ return pmd_offset(pudp, addr);
+}
+
+/*
+ * hugetlb_alloc_pte -- Allocate a PTE beneath a pmd_none PMD-level hpte.
+ *
+ * See the comment above hugetlb_alloc_pmd.
+ */
+pte_t *hugetlb_alloc_pte(struct mm_struct *mm, struct hugetlb_pte *hpte,
+ unsigned long addr)
+{
+ spinlock_t *ptl = hugetlb_pte_lockptr(hpte);
+ pgtable_t new;
+ pmd_t *pmdp;
+ pmd_t pmd;
+
+ if (hpte->level != HUGETLB_LEVEL_PMD)
+ return ERR_PTR(-EINVAL);
+
+ pmdp = (pmd_t *)hpte->ptep;
+retry:
+ pmd = READ_ONCE(*pmdp);
+ if (likely(pmd_present(pmd)))
+ return unlikely(pmd_leaf(pmd))
+ ? ERR_PTR(-EEXIST)
+ : pte_offset_kernel(pmdp, addr);
+ else if (!pmd_none(pmd))
+ /*
+ * Not present and not none means that a swap entry lives here,
+ * and we can't get rid of it.
+ */
+ return ERR_PTR(-EEXIST);
+
+ /*
+ * With CONFIG_HIGHPTE, calling `pte_alloc_one` directly may result
+ * in page tables being allocated in high memory, needing a kmap to
+ * access. Instead, we call __pte_alloc_one directly with
+ * GFP_PGTABLE_USER to prevent these PTEs being allocated in high
+ * memory.
+ */
+ new = __pte_alloc_one(mm, GFP_PGTABLE_USER);
+ if (!new)
+ return ERR_PTR(-ENOMEM);
+
+ spin_lock(ptl);
+ if (!pmd_same(pmd, *pmdp)) {
+ spin_unlock(ptl);
+ pgtable_pte_page_dtor(new);
+ __free_page(new);
+ goto retry;
+ }
+
+ mm_inc_nr_ptes(mm);
+ smp_wmb(); /* See comment in pmd_install() */
+ pmd_populate(mm, pmdp, new);
+ spin_unlock(ptl);
+ return pte_offset_kernel(pmdp, addr);
+}
+
static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
{
struct file_region *nrg, *prg;
--
2.39.0.314.g84b9a713c41-goog
