Commit eb2faa51 authored Aug 13, 2021 by David Hildenbrand Committed by Linus Torvalds Aug 13, 2021

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 behavior.

Link: https://lkml.kernel.org/r/20210726154932.102880-1-david@redhat.com


Fixes: 4ca9b385 ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables")
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rolf Eike Beer <eike-kernel@sf-tec.de>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent a7f1d485

mm/gup.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -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);
		}

mm/madvise.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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);