This is a note to let you know that I've just added the patch titled
mips,s390,sh,sparc: gup: Work around the "COW can break either way" issue
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mips-s390-sh-sparc-gup-work-around-the-cow-can-break-either-way-issue.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From ben@xxxxxxxxxxxxxxx Mon Jan 24 16:18:27 2022
From: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Date: Mon, 24 Jan 2022 16:11:18 +0100
Subject: mips,s390,sh,sparc: gup: Work around the "COW can break either way" issue
To: stable@xxxxxxxxxxxxxxx
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Message-ID: <Ye7BluXgj+5i9VUb@xxxxxxxxxxxxxxx>
Content-Disposition: inline
From: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
---
arch/mips/mm/gup.c | 9 ++++++++-
arch/s390/mm/gup.c | 9 ++++++++-
arch/sh/mm/gup.c | 9 ++++++++-
arch/sparc/mm/gup.c | 9 ++++++++-
4 files changed, 32 insertions(+), 4 deletions(-)
--- a/arch/mips/mm/gup.c
+++ b/arch/mips/mm/gup.c
@@ -272,7 +272,14 @@ int get_user_pages_fast(unsigned long st
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();
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -285,7 +285,14 @@ int get_user_pages_fast(unsigned long st
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;
--- a/arch/sh/mm/gup.c
+++ b/arch/sh/mm/gup.c
@@ -240,7 +240,14 @@ int get_user_pages_fast(unsigned long st
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();
--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -262,7 +262,14 @@ int get_user_pages_fast(unsigned long st
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);
Patches currently in stable-queue which might be from ben@xxxxxxxxxxxxxxx are
queue-4.14/mips-s390-sh-sparc-gup-work-around-the-cow-can-break-either-way-issue.patch
queue-4.14/firmware-update-kconfig-help-text-for-google-firmware.patch
