• Jason Baron's avatar
    coredump: remove VM_ALWAYSDUMP flag · 909af768
    Jason Baron authored
    The motivation for this patchset was that I was looking at a way for a
    qemu-kvm process, to exclude the guest memory from its core dump, which
    can be quite large.  There are already a number of filter flags in
    /proc/<pid>/coredump_filter, however, these allow one to specify 'types'
    of kernel memory, not specific address ranges (which is needed in this
    case).
    
    Since there are no more vma flags available, the first patch eliminates
    the need for the 'VM_ALWAYSDUMP' flag.  The flag is used internally by
    the kernel to mark vdso and vsyscall pages.  However, it is simple
    enough to check if a vma covers a vdso or vsyscall page without the need
    for this flag.
    
    The second patch then replaces the 'VM_ALWAYSDUMP' flag with a new
    'VM_NODUMP' flag, which can be set by userspace using new madvise flags:
    'MADV_DONTDUMP', and unset via 'MADV_DODUMP'.  The core dump filters
    continue to work the same as before unless 'MADV_DONTDUMP' is set on the
    region.
    
    The qemu code which implements this features is at:
    
      http://people.redhat.com/~jbaron/qemu-dump/qemu-dump.patch
    
    In my testing the qemu core dump shrunk from 383MB -> 13MB with this
    patch.
    
    I also believe that the 'MADV_DONTDUMP' flag might be useful for
    security sensitive apps, which might want to select which areas are
    dumped.
    
    This patch:
    
    The VM_ALWAYSDUMP flag is currently used by the coredump code to
    indicate that a vma is part of a vsyscall or vdso section.  However, we
    can determine if a vma is in one these sections by checking it against
    the gate_vma and checking for a non-NULL return value from
    arch_vma_name().  Thus, freeing a valuable vma bit.
    Signed-off-by: default avatarJason Baron <jbaron@redhat.com>
    Acked-by: default avatarRoland McGrath <roland@hack.frob.com>
    Cc: Chris Metcalf <cmetcalf@tilera.com>
    Cc: Avi Kivity <avi@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    909af768
process.c 12.8 KB