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>
Cc: x86@xxxxxxxxxx
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Tested-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
arch/x86/include/asm/pgtable.h | 7 ++++
arch/x86/mm/gup.c | 57 +++++++++++++++++++++++++++++-
include/linux/huge_mm.h | 10 +++++
include/linux/mm.h | 42 +++++++++++++++++-----
kernel/memremap.c | 20 +++++++++++
mm/gup.c | 19 ++++++++++
mm/huge_memory.c | 75 ++++++++++++++++++++++++++++++++--------
mm/swap.c | 3 ++
8 files changed, 202 insertions(+), 31 deletions(-)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 993ce3c84ff4..40fe31853f07 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -482,6 +482,13 @@ static inline int pte_present(pte_t a)
return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE);
}
+#ifdef __HAVE_ARCH_PTE_DEVMAP
+static inline int pte_devmap(pte_t a)
+{
+ return (pte_flags(a) & _PAGE_DEVMAP) == _PAGE_DEVMAP;
+}
+#endif
+
#define pte_accessible pte_accessible
static inline bool pte_accessible(struct mm_struct *mm, pte_t a)
{
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index f8cb3e8ac250..6d5eb5900372 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -9,6 +9,7 @@
#include <linux/vmstat.h>
#include <linux/highmem.h>
#include <linux/swap.h>
+#include <linux/memremap.h>
#include <asm/pgtable.h>
@@ -63,6 +64,16 @@ 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 +82,9 @@ 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 +102,21 @@ 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 +135,32 @@ 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 +173,13 @@ 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 40c4db60c9e0..bc141a65b736 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -38,7 +38,6 @@ 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,
@@ -55,6 +54,9 @@ enum transparent_hugepage_flag {
#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))
@@ -205,6 +207,12 @@ 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 96f396bbcc9f..be0c31362baf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -16,6 +16,7 @@
#include <linux/mm_types.h>
#include <linux/range.h>
#include <linux/pfn.h>
+#include <linux/percpu-refcount.h>
#include <linux/bit_spinlock.h>
#include <linux/shrinker.h>
#include <linux/resource.h>
@@ -470,17 +471,6 @@ static inline int page_count(struct page *page)
return atomic_read(&compound_head(page)->_count);
}
-static inline void get_page(struct page *page)
-{
- page = compound_head(page);
- /*
- * 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);
@@ -687,17 +677,40 @@ static inline enum zone_type page_zonenum(const struct page *page)
}
#ifdef CONFIG_ZONE_DEVICE
+void get_zone_device_page(struct page *page);
+int release_zone_device_page(struct page *page);
static inline bool is_zone_device_page(const struct page *page)
{
return page_zonenum(page) == ZONE_DEVICE;
}
#else
+static inline void get_zone_device_page(struct page *page)
+{
+}
+static inline int release_zone_device_page(struct page *page)
+{
+ return 0;
+}
static inline bool is_zone_device_page(const struct page *page)
{
return false;
}
#endif
+static inline void get_page(struct page *page)
+{
+ page = compound_head(page);
+ /*
+ * 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 (unlikely(is_zone_device_page(page)))
+ get_zone_device_page(page);
+}
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
@@ -1478,6 +1491,13 @@ static inline int pmd_devmap(pmd_t pmd)
}
#endif
+#ifndef __HAVE_ARCH_PTE_DEVMAP
+static inline int pte_devmap(pte_t pte)
+{
+ return 0;
+}
+#endif
+
#if defined(__PAGETABLE_PMD_FOLDED) || !defined(CONFIG_MMU)
static inline int __pmd_alloc(struct mm_struct *mm, pud_t *pud,
unsigned long address)
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 3eb8944265d5..ccbb4beeaa71 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -169,6 +169,26 @@ struct page_map {
struct vmem_altmap altmap;
};
+void get_zone_device_page(struct page *page)
+{
+ percpu_ref_get(page->pgmap->ref);
+}
+EXPORT_SYMBOL(get_zone_device_page);
+
+int release_zone_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;
+}
+EXPORT_SYMBOL(release_zone_device_page);
+
static void pgmap_radix_release(struct resource *res)
{
resource_size_t key;
diff --git a/mm/gup.c b/mm/gup.c
index e95b0cb6ed81..a484e0df88b6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -4,6 +4,7 @@
#include <linux/spinlock.h>
#include <linux/mm.h>
+#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
@@ -98,7 +99,16 @@ 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);
@@ -237,6 +247,13 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
}
if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
return no_page_table(vma, flags);
+ if (pmd_devmap(*pmd)) {
+ ptl = pmd_lock(mm, pmd);
+ page = follow_devmap_pmd(vma, address, pmd, flags);
+ spin_unlock(ptl);
+ if (page)
+ return page;
+ }
if (likely(!pmd_trans_huge(*pmd)))
return follow_page_pte(vma, address, pmd, flags);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0c114fa08349..5fd0c4a30ae9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -22,6 +22,7 @@
#include <linux/freezer.h>
#include <linux/pfn_t.h>
#include <linux/mman.h>
+#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/migrate.h>
#include <linux/hashtable.h>
@@ -1003,6 +1004,63 @@ 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));
+
+ 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);
+
+ /*
+ * device mapped pages can only be returned if the
+ * caller will manage the page reference count.
+ */
+ if (!(flags & FOLL_GET))
+ return ERR_PTR(-EEXIST);
+
+ 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)
@@ -1360,21 +1418,8 @@ 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)) {
/*
* We don't mlock() pte-mapped THPs. This way we can avoid
diff --git a/mm/swap.c b/mm/swap.c
index 674e2c93da4e..9a6e3db20e59 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -24,6 +24,7 @@
#include <linux/export.h>
#include <linux/mm_inline.h>
#include <linux/percpu_counter.h>
+#include <linux/memremap.h>
#include <linux/percpu.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
@@ -94,6 +95,8 @@ void __put_page(struct page *page)
{
if (unlikely(PageCompound(page)))
__put_compound_page(page);
+ else if (unlikely(is_zone_device_page(page)))
+ release_zone_device_page(page);
else
__put_single_page(page);
}
--
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