[RESEND 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast

ira.weiny
2019-03-17T18:34:35Z

From: Ira Weiny <ira.weiny@intel.com>

DAX pages were previously unprotected from longterm pins when users
called get_user_pages_fast().

Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall
back to regular GUP processing if a DEVMAP page is encountered.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
mm/gup.c | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 0684a9536207..173db0c44678 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1600,6 +1600,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
goto pte_unmap;

if (pte_devmap(pte)) {
+ if (unlikely(flags & FOLL_LONGTERM))
+ goto pte_unmap;
+
pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
if (unlikely(!pgmap)) {
undo_dev_pagemap(nr, nr_start, pages);
@@ -1739,8 +1742,11 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
return 0;

- if (pmd_devmap(orig))
+ if (pmd_devmap(orig)) {
+ if (unlikely(flags & FOLL_LONGTERM))
+ return 0;
return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
+ }

refs = 0;
page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
@@ -1777,8 +1783,11 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
if (!pud_access_permitted(orig, flags & FOLL_WRITE))
return 0;

- if (pud_devmap(orig))
+ if (pud_devmap(orig)) {
+ if (unlikely(flags & FOLL_LONGTERM))
+ return 0;
return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr);
+ }

refs = 0;
page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
@@ -2066,8 +2075,20 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
start += nr << PAGE_SHIFT;
pages += nr;

- ret = get_user_pages_unlocked(start, nr_pages - nr, pages,
- gup_flags);
+ if (gup_flags & FOLL_LONGTERM) {
+ down_read(&current->mm->mmap_sem);
+ ret = __gup_longterm_locked(current, current->mm,
+ start, nr_pages - nr,
+ pages, NULL, gup_flags);
+ up_read(&current->mm->mmap_sem);
+ } else {
+ /*
+ * retain FAULT_FOLL_ALLOW_RETRY optimization if
+ * possible
+ */
+ ret = get_user_pages_unlocked(start, nr_pages - nr,
+ pages, gup_flags);
+ }

/* Have to be a bit careful with return values */
if (nr > 0) {
--
2.20.1