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Message-Id: <20220124183950.633915249@linuxfoundation.org>
Date: Mon, 24 Jan 2022 19:44:35 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Ben Hutchings <ben@...adent.org.uk>
Subject: [PATCH 4.19 237/239] mips,s390,sh,sparc: gup: Work around the "COW can break either way" issue
From: Ben Hutchings <ben@...adent.org.uk>
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@...adent.org.uk>
---
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
@@ -274,7 +274,14 @@ 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
@@ -287,7 +287,14 @@ 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
@@ -242,7 +242,14 @@ 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
@@ -303,7 +303,14 @@ 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);
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