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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: 407faed92b ("gup: document and work around "COW can break either way" issue")
Fixes: 5e24029791 ("gup: document and work around "COW can break either way" issue")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Ben Hutchings 2022-01-24 16:11:18 +01:00 committed by Greg Kroah-Hartman
parent 04d1dbd1e8
commit 70b5928f5c
4 changed files with 32 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
arch/mips/mm/gup.c
View File

@ -272,7 +272,14 @@ 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();

9
arch/s390/mm/gup.c
View File

@ -285,7 +285,14 @@ 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;

9
arch/sh/mm/gup.c
View File

@ -240,7 +240,14 @@ 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();

9
arch/sparc/mm/gup.c
View File

@ -262,7 +262,14 @@ 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);