mips,s390,sh,sparc: gup: Work around the "COW can break either way" issue

In Linux 4.14 and 4.19 these architectures still have their own
implementations of get_user_pages_fast().  These also need to force
the write flag on when taking the fast path.

Fixes: 407faed92b4a ("gup: document and work around "COW can break either way" issue")
Fixes: 5e24029791e8 ("gup: document and work around "COW can break either way" issue")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/mips/mm/gup.c b/arch/mips/mm/gup.c
index 5a4875cac1ec979da60be7ed3f80379eab5d6b65..2e7a0d201c09eb7deb7f1af9c621dc7d1cf6e6c3 100644 (file)
--- a/arch/mips/mm/gup.c
+++ b/arch/mips/mm/gup.c
@@ -274,7 +274,14 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        goto slow;
-               if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
+               /*
+                * The FAST_GUP case requires FOLL_WRITE even for pure reads,
+                * because get_user_pages() may need to cause an early COW in
+                * order to avoid confusing the normal COW routines. So only
+                * targets that are already writable are safe to do by just
+                * looking at the page tables.
+                */
+               if (!gup_pud_range(pgd, addr, next, 1, pages, &nr))
                        goto slow;
        } while (pgdp++, addr = next, addr != end);
        local_irq_enable();

diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
index 9b5b866d8adf1025b2f0fff05fdd938ce4af727f..5389bf5bc828369c1979362bbb73ba2fb1a66381 100644 (file)
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -287,7 +287,14 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 
        might_sleep();
        start &= PAGE_MASK;
-       nr = __get_user_pages_fast(start, nr_pages, write, pages);
+       /*
+        * The FAST_GUP case requires FOLL_WRITE even for pure reads,
+        * because get_user_pages() may need to cause an early COW in
+        * order to avoid confusing the normal COW routines. So only
+        * targets that are already writable are safe to do by just
+        * looking at the page tables.
+        */
+       nr = __get_user_pages_fast(start, nr_pages, 1, pages);
        if (nr == nr_pages)
                return nr;
 

diff --git a/arch/sh/mm/gup.c b/arch/sh/mm/gup.c
index 56c86ca98ecfe774eecf197af16aa90240423e15..23fa2fc8aabc4482f117cf16649b06e90f4bb6a0 100644 (file)
--- a/arch/sh/mm/gup.c
+++ b/arch/sh/mm/gup.c
@@ -242,7 +242,14 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        goto slow;
-               if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
+               /*
+                * The FAST_GUP case requires FOLL_WRITE even for pure reads,
+                * because get_user_pages() may need to cause an early COW in
+                * order to avoid confusing the normal COW routines. So only
+                * targets that are already writable are safe to do by just
+                * looking at the page tables.
+                */
+               if (!gup_pud_range(pgd, addr, next, 1, pages, &nr))
                        goto slow;
        } while (pgdp++, addr = next, addr != end);
        local_irq_enable();

diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
index aee6dba83d0eceed0c3554bafdb5d053f12df64c..f291d34a1cd5e2312c320b9dbf465c100dccce46 100644 (file)
--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -303,7 +303,14 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
                next = pgd_addr_end(addr, end);
                if (pgd_none(pgd))
                        goto slow;
-               if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
+               /*
+                * The FAST_GUP case requires FOLL_WRITE even for pure reads,
+                * because get_user_pages() may need to cause an early COW in
+                * order to avoid confusing the normal COW routines. So only
+                * targets that are already writable are safe to do by just
+                * looking at the page tables.
+                */
+               if (!gup_pud_range(pgd, addr, next, 1, pages, &nr))
                        goto slow;
        } while (pgdp++, addr = next, addr != end);