mm, x86: get_user_pages() for dax mappings
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().
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 82bed2b..b2db981 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -23,6 +23,7 @@
#include <linux/freezer.h>
#include <linux/pfn_t.h>
#include <linux/mman.h>
+#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/debugfs.h>
#include <linux/migrate.h>
@@ -974,6 +975,63 @@
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)
@@ -1331,21 +1389,8 @@
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