From: David Hildenbrand <david@xxxxxxxxxx> Subject: mm/madvise: report SIGBUS as -EFAULT for MADV_POPULATE_(READ|WRITE) 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 behavio= r. Link: https://lkml.kernel.org/r/20210726154932.102880-1-david@xxxxxxxxxx Fixes: 4ca9b3859dac ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables") Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> 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: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 7 +++++-- mm/madvise.c | 4 +++- 2 files changed, 8 insertions(+), 3 deletions(-) --- a/mm/gup.c~mm-madvise-report-sigbus-as-efault-for-madv_populate_readwrite +++ a/mm/gup.c @@ -1558,9 +1558,12 @@ long faultin_vma_page_range(struct vm_ar 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); } --- a/mm/madvise.c~mm-madvise-report-sigbus-as-efault-for-madv_populate_readwrite +++ a/mm/madvise.c @@ -862,10 +862,12 @@ static long madvise_populate(struct vm_a 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); _
