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Subject[PATCH V3 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast
Date
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>

---
Changes from V2:
Add comment on special use case of FOLL_LONGTERM

mm/gup.c | 40 ++++++++++++++++++++++++++++++++++++----
1 file changed, 36 insertions(+), 4 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 0fa7244d6f19..567bd1b295f0 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1613,6 +1613,9 @@ 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);
@@ -1752,8 +1755,11 @@ 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);
@@ -1790,8 +1796,11 @@ 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);
@@ -2034,6 +2043,29 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
return nr;
}

+static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
+ unsigned int gup_flags, struct page **pages)
+{
+ int ret;
+
+ /*
+ * FIXME: FOLL_LONGTERM does not work with
+ * get_user_pages_unlocked() (see comments in that function)
+ */
+ if (gup_flags & FOLL_LONGTERM) {
+ down_read(&current->mm->mmap_sem);
+ ret = __gup_longterm_locked(current, current->mm,
+ start, nr_pages,
+ pages, NULL, gup_flags);
+ up_read(&current->mm->mmap_sem);
+ } else {
+ ret = get_user_pages_unlocked(start, nr_pages,
+ pages, gup_flags);
+ }
+
+ return ret;
+}
+
/**
* get_user_pages_fast() - pin user pages in memory
* @start: starting user address
@@ -2079,8 +2111,8 @@ 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);
+ ret = __gup_longterm_unlocked(start, nr_pages - nr,
+ gup_flags, pages);

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