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Subject[PATCH 5/7] mm/gup: Implement dev_pagemap logic in generic get_user_pages_fast()
Date
This is preparation patch for transition of x86 to generic GUP_fast()
implementation.

Prepare generic GUP_fast() to handle dev_mapmap. At the moment, it's
only implemented on x86. On non-x86, the new code will be compiled out.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
---
include/linux/mm.h | 4 +++
mm/gup.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 75 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5f01c88f0800..e197d3ca3e8a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -430,6 +430,10 @@ static inline int pud_devmap(pud_t pud)
{
return 0;
}
+static inline int pgd_devmap(pgd_t pgd)
+{
+ return 0;
+}
#endif

/*
diff --git a/mm/gup.c b/mm/gup.c
index f0cfe225c08f..e04f76594eb9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1200,12 +1200,23 @@ static inline pte_t gup_get_pte(pte_t *ptep)
}
#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);
+ }
+}
+
#ifdef __HAVE_ARCH_PTE_SPECIAL
static 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;
+ int nr_start = *nr, ret = 0;
pte_t *ptep, *ptem;
- int ret = 0;

ptem = ptep = pte_offset_map(&pmd, addr);
do {
@@ -1222,7 +1233,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
if (!pte_access_permitted(pte, write))
goto pte_unmap;

- if (pte_special(pte))
+ if (pte_devmap(pte)) {
+ pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
+ if (unlikely(!pgmap)) {
+ undo_dev_pagemap(nr, nr_start, pages);
+ goto pte_unmap;
+ }
+ } else if (pte_special(pte))
goto pte_unmap;

VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
@@ -1239,6 +1256,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,

VM_BUG_ON_PAGE(compound_head(page) != head, page);

+ put_dev_pagemap(pgmap);
SetPageReferenced(page);
pages[*nr] = page;
(*nr)++;
@@ -1269,6 +1287,48 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
}
#endif /* __HAVE_ARCH_PTE_SPECIAL */

+static int __gup_device_huge(unsigned long pfn, unsigned long addr,
+ unsigned long end, struct page **pages, int *nr)
+{
+ int nr_start = *nr;
+ struct dev_pagemap *pgmap = NULL;
+
+ 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 int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
+ unsigned long end, struct page **pages, int *nr)
+{
+ unsigned long fault_pfn;
+
+ fault_pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+ return __gup_device_huge(fault_pfn, addr, end, pages, nr);
+}
+
+static int __gup_device_huge_pud(pud_t pud, unsigned long addr,
+ unsigned long end, struct page **pages, int *nr)
+{
+ unsigned long fault_pfn;
+
+ fault_pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
+ return __gup_device_huge(fault_pfn, addr, end, pages, nr);
+}
+
static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
@@ -1278,6 +1338,10 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
if (!pmd_access_permitted(orig, write))
return 0;

+ VM_BUG_ON(!pfn_valid(pmd_pfn(orig)));
+ if (pmd_devmap(orig))
+ return __gup_device_huge_pmd(orig, addr, end, pages, nr);
+
refs = 0;
head = pmd_page(orig);
page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
@@ -1314,6 +1378,10 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
if (!pud_access_permitted(orig, write))
return 0;

+ VM_BUG_ON(!pfn_valid(pud_pfn(orig)));
+ if (pud_devmap(orig))
+ return __gup_device_huge_pud(orig, addr, end, pages, nr);
+
refs = 0;
head = pud_page(orig);
page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
@@ -1351,6 +1419,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
if (!pgd_access_permitted(orig, write))
return 0;

+ BUILD_BUG_ON(pgd_devmap(orig));
refs = 0;
head = pgd_page(orig);
page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
--
2.11.0
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