A dax mapping establishes a pte with _PAGE_DEVMAP set when the driver
has established a devm_memremap_pages() mapping, i.e. when the pfn_t
return from ->direct_access() has PFN_DEV and PFN_MAP set. Later, when
encountering _PAGE_DEVMAP during a page table walk we lookup and pin a
struct dev_pagemap instance to keep the result of pfn_to_page() valid
until put_page().
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
arch/x86/mm/gup.c | 56 ++++++++++++++++++++++++++++++++++--
include/linux/huge_mm.h | 10 ++++++
include/linux/mm.h | 40 +++++++++++++++++--------
mm/gup.c | 17 ++++++++++-
mm/huge_memory.c | 74 +++++++++++++++++++++++++++++++++++++----------
mm/swap.c | 15 ++++++++++
6 files changed, 179 insertions(+), 33 deletions(-)
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index ae9a37bf1371..9fa9e8be6e70 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -63,6 +63,16 @@ retry:
#endif
}
+static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
+{
+ while ((*nr) - nr_start) {
+ struct page *page = pages[--(*nr)];
+
+ ClearPageReferenced(page);
+ put_page(page);
+ }
+}
+
/*
* The performance critical leaf functions are made noinline otherwise gcc
* inlines everything into a single function which results in too much
@@ -71,7 +81,9 @@ retry:
static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
+ struct dev_pagemap *pgmap = NULL;
unsigned long mask;
+ int nr_start = *nr;
pte_t *ptep;
mask = _PAGE_PRESENT|_PAGE_USER;
@@ -89,13 +101,21 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
return 0;
}
- if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
+ page = pte_page(pte);
+ if (pte_devmap(pte)) {
+ pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
+ if (unlikely(!pgmap)) {
+ undo_dev_pagemap(nr, nr_start, pages);
+ pte_unmap(ptep);
+ return 0;
+ }
+ } else if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
pte_unmap(ptep);
return 0;
}
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
- page = pte_page(pte);
get_page(page);
+ put_dev_pagemap(pgmap);
SetPageReferenced(page);
pages[*nr] = page;
(*nr)++;
@@ -114,6 +134,32 @@ static inline void get_head_page_multiple(struct page *page, int nr)
SetPageReferenced(page);
}
+static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
+ unsigned long end, struct page **pages, int *nr)
+{
+ int nr_start = *nr;
+ unsigned long pfn = pmd_pfn(pmd);
+ struct dev_pagemap *pgmap = NULL;
+
+ pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
+ do {
+ struct page *page = pfn_to_page(pfn);
+
+ pgmap = get_dev_pagemap(pfn, pgmap);
+ if (unlikely(!pgmap)) {
+ undo_dev_pagemap(nr, nr_start, pages);
+ return 0;
+ }
+ SetPageReferenced(page);
+ pages[*nr] = page;
+ get_page(page);
+ put_dev_pagemap(pgmap);
+ (*nr)++;
+ pfn++;
+ } while (addr += PAGE_SIZE, addr != end);
+ return 1;
+}
+
static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
@@ -126,9 +172,13 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
mask |= _PAGE_RW;
if ((pmd_flags(pmd) & mask) != mask)
return 0;
+
+ VM_BUG_ON(!pfn_valid(pmd_pfn(pmd)));
+ if (pmd_devmap(pmd))
+ return __gup_device_huge_pmd(pmd, addr, end, pages, nr);
+
/* hugepages are never "special" */
VM_BUG_ON(pmd_flags(pmd) & _PAGE_SPECIAL);
- VM_BUG_ON(!pfn_valid(pmd_pfn(pmd)));
refs = 0;
head = pmd_page(pmd);
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 9c9c1688889a..9278ba57b390 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -35,7 +35,6 @@ extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
int prot_numa);
int vmf_insert_pfn_pmd(struct vm_area_struct *, unsigned long addr, pmd_t *,
pfn_t pfn, bool write);
-
enum transparent_hugepage_flag {
TRANSPARENT_HUGEPAGE_FLAG,
TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
@@ -63,6 +62,9 @@ extern pmd_t *page_check_address_pmd(struct page *page,
#define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
+ pmd_t *pmd, int flags);
+
#define HPAGE_PMD_SHIFT PMD_SHIFT
#define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT)
#define HPAGE_PMD_MASK (~(HPAGE_PMD_SIZE - 1))
@@ -219,6 +221,12 @@ static inline bool is_huge_zero_page(struct page *page)
return false;
}
+
+static inline struct page *follow_devmap_pmd(struct vm_area_struct *vma,
+ unsigned long addr, pmd_t *pmd, int flags)
+{
+ return NULL;
+}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif /* _LINUX_HUGE_MM_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f985d181e730..40ee1d17f847 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -486,19 +486,6 @@ static inline void get_huge_page_tail(struct page *page)
extern bool __get_page_tail(struct page *page);
-static inline void get_page(struct page *page)
-{
- if (unlikely(PageTail(page)))
- if (likely(__get_page_tail(page)))
- return;
- /*
- * Getting a normal page or the head of a compound page
- * requires to already have an elevated page->_count.
- */
- VM_BUG_ON_PAGE(atomic_read(&page->_count) <= 0, page);
- atomic_inc(&page->_count);
-}
-
static inline struct page *virt_to_head_page(const void *x)
{
struct page *page = virt_to_page(x);
@@ -777,6 +764,11 @@ struct dev_pagemap {
void *devm_memremap_pages(struct device *dev, struct resource *res,
struct percpu_ref *ref, struct vmem_altmap *altmap);
struct dev_pagemap *find_dev_pagemap(resource_size_t phys);
+
+static inline bool is_zone_device_page(const struct page *page)
+{
+ return page_zonenum(page) == ZONE_DEVICE;
+}
#else
static inline void *devm_memremap_pages(struct device *dev,
struct resource *res, struct percpu_ref *ref,
@@ -795,6 +787,11 @@ static inline struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
{
return NULL;
}
+
+static inline bool is_zone_device_page(const struct page *page)
+{
+ return false;
+}
#endif
#if defined(CONFIG_SPARSEMEM_VMEMMAP) && defined(CONFIG_ZONE_DEVICE)
@@ -845,6 +842,23 @@ static inline void put_dev_pagemap(struct dev_pagemap *pgmap)
percpu_ref_put(pgmap->ref);
}
+static inline void get_page(struct page *page)
+{
+ if (unlikely(PageTail(page)))
+ if (likely(__get_page_tail(page)))
+ return;
+
+ if (is_zone_device_page(page))
+ percpu_ref_get(page->pgmap->ref);
+
+ /*
+ * Getting a normal page or the head of a compound page
+ * requires to already have an elevated page->_count.
+ */
+ VM_BUG_ON_PAGE(atomic_read(&page->_count) <= 0, page);
+ atomic_inc(&page->_count);
+}
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
diff --git a/mm/gup.c b/mm/gup.c
index deafa2c91b36..32514c179830 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -98,7 +98,16 @@ retry:
}
page = vm_normal_page(vma, address, pte);
- if (unlikely(!page)) {
+ if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
+ /*
+ * Only return device mapping pages in the FOLL_GET case since
+ * they are only valid while holding the pgmap reference.
+ */
+ if (get_dev_pagemap(pte_pfn(pte), NULL))
+ page = pte_page(pte);
+ else
+ goto no_page;
+ } else if (unlikely(!page)) {
if (flags & FOLL_DUMP) {
/* Avoid special (like zero) pages in core dumps */
page = ERR_PTR(-EFAULT);
@@ -240,6 +249,12 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
} else
spin_unlock(ptl);
}
+ if (pmd_devmap(*pmd)) {
+ ptl = pmd_lock(mm, pmd);
+ page = follow_devmap_pmd(vma, address, pmd, flags);
+ spin_unlock(ptl);
+ return page;
+ }
return follow_page_pte(vma, address, pmd, flags);
}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 329cedf48b8a..f0b020e65547 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -912,6 +912,63 @@ int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
return VM_FAULT_NOPAGE;
}
+static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
+ pmd_t *pmd)
+{
+ 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));
+ if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
+ pmd, _pmd, 1))
+ update_mmu_cache_pmd(vma, addr, pmd);
+}
+
+struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
+ pmd_t *pmd, int flags)
+{
+ unsigned long pfn = pmd_pfn(*pmd);
+ struct mm_struct *mm = vma->vm_mm;
+ struct dev_pagemap *pgmap;
+ struct page *page;
+
+ assert_spin_locked(pmd_lockptr(mm, pmd));
+
+ /*
+ * device mapped pages can only be returned if the
+ * caller will manage the page reference count.
+ */
+ if (!(flags & FOLL_GET))
+ return NULL;
+
+ if (flags & FOLL_WRITE && !pmd_write(*pmd))
+ return NULL;
+
+ if (pmd_present(*pmd) && pmd_devmap(*pmd))
+ /* pass */;
+ else
+ return NULL;
+
+ if (flags & FOLL_TOUCH)
+ touch_pmd(vma, addr, pmd);
+
+ pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
+ pgmap = get_dev_pagemap(pfn, NULL);
+ if (!pgmap)
+ return ERR_PTR(-EFAULT);
+ page = pfn_to_page(pfn);
+ get_page(page);
+ put_dev_pagemap(pgmap);
+
+ return page;
+}
+
int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
struct vm_area_struct *vma)
@@ -1295,21 +1352,8 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
page = pmd_page(*pmd);
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));
- if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
- pmd, _pmd, 1))
- update_mmu_cache_pmd(vma, addr, pmd);
- }
+ if (flags & FOLL_TOUCH)
+ touch_pmd(vma, addr, pmd);
if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
if (page->mapping && trylock_page(page)) {
lru_add_drain();
diff --git a/mm/swap.c b/mm/swap.c
index 39395fb549c0..1d1d4309aff6 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -230,6 +230,19 @@ out_put_single:
}
}
+static bool put_device_page(struct page *page)
+{
+ /*
+ * ZONE_DEVICE pages are never "onlined" so their reference
+ * counts never reach zero. They are always owned by a device
+ * driver, not the mm core. I.e. the page is 'idle' when the
+ * count is 1.
+ */
+ VM_BUG_ON_PAGE(atomic_read(&page->_count) == 1, page);
+ put_dev_pagemap(page->pgmap);
+ return atomic_dec_return(&page->_count) == 1;
+}
+
static void put_compound_page(struct page *page)
{
struct page *page_head;
@@ -273,6 +286,8 @@ void put_page(struct page *page)
{
if (unlikely(PageCompound(page)))
put_compound_page(page);
+ else if (is_zone_device_page(page))
+ put_device_page(page);
else if (put_page_testzero(page))
__put_single_page(page);
}
--
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