| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.19 237/239] mips,s390,sh,sparc: gup: Work around the "COW can break either way" issue | Date | Mon, 24 Jan 2022 19:44:35 +0100 |
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From: Ben Hutchings <ben@decadent.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@decadent.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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