Hi Andrew,
sorry for not CCing you, absolutely no clue why I accidentally dropped
you. Can you give this patch a churn? It would be great if we could get
that into 5.14, so we don't have to deal with differing behavior between
Linux versions.
Cheers!
On 26.07.21 17:49, David Hildenbrand wrote:
Doing some extended tests and polishing the man page update for
MADV_POPULATE_(READ|WRITE), I realized that we end up converting also
SIGBUS (via -EFAULT) to -EINVAL, making it look like yet another
madvise() user error.
We want to report only problematic mappings and permission problems that
the user could have know as -EINVAL.
Let's not convert -EFAULT arising due to SIGBUS (or SIGSEGV) to
-EINVAL, but instead indicate -EFAULT to user space. While we could also
convert it to -ENOMEM, using -EFAULT looks more helpful when user space
might want to troubleshoot what's going wrong: MADV_POPULATE_(READ|WRITE)
is not part of an final Linux release and we can still adjust the behavior.
Fixes: 4ca9b3859dac ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables")
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Richard Henderson <rth@xxxxxxxxxxx>
Cc: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>
Cc: Matt Turner <mattst88@xxxxxxxxx>
Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Cc: "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: Chris Zankel <chris@xxxxxxxxxx>
Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Rolf Eike Beer <eike-kernel@xxxxxxxxx>
Cc: Ram Pai <linuxram@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/gup.c | 7 +++++--
mm/madvise.c | 4 +++-
2 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 42b8b1fa6521..b94717977d17 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1558,9 +1558,12 @@ long faultin_vma_page_range(struct vm_area_struct *vma, unsigned long start,
gup_flags |= FOLL_WRITE;
/*
- * See check_vma_flags(): Will return -EFAULT on incompatible mappings
- * or with insufficient permissions.
+ * We want to report -EINVAL instead of -EFAULT for any permission
+ * problems or incompatible mappings.
*/
+ if (check_vma_flags(vma, gup_flags))
+ return -EINVAL;
+
return __get_user_pages(mm, start, nr_pages, gup_flags,
NULL, NULL, locked);
}
diff --git a/mm/madvise.c b/mm/madvise.c
index 6d3d348b17f4..5c065bc8b5f6 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -862,10 +862,12 @@ static long madvise_populate(struct vm_area_struct *vma,
switch (pages) {
case -EINTR:
return -EINTR;
- case -EFAULT: /* Incompatible mappings / permissions. */
+ case -EINVAL: /* Incompatible mappings / permissions. */
return -EINVAL;
case -EHWPOISON:
return -EHWPOISON;
+ case -EFAULT: /* VM_FAULT_SIGBUS or VM_FAULT_SIGSEGV */
+ return -EFAULT;
default:
pr_warn_once("%s: unhandled return value: %ld\n",
__func__, pages);
--
Thanks,
David / dhildenb
