linux/arch/s390
Jason Baron 909af768e8 coredump: remove VM_ALWAYSDUMP flag
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: Jason Baron <jbaron@redhat.com>
Acked-by: Roland McGrath <roland@hack.frob.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-03-23 16:58:42 -07:00
..
appldata sched/accounting: Change cpustat fields to an array 2011-12-06 09:06:38 +01:00
boot [S390] Remove Kerntypes leftovers 2011-12-27 11:27:12 +01:00
crypto [S390] crypto: avoid MSA3 and MSA4 instructions in ESA mode 2011-11-14 11:19:09 +01:00
hypfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
include/asm Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2012-03-22 18:15:32 -07:00
kernel coredump: remove VM_ALWAYSDUMP flag 2012-03-23 16:58:42 -07:00
kvm [S390] rename lowcore field 2012-03-11 11:59:27 -04:00
lib [S390] rework idle code 2012-03-11 11:59:28 -04:00
math-emu s390: change to new flag variable 2011-03-17 14:02:57 +01:00
mm [S390] irq: external interrupt code passing 2012-03-11 11:59:29 -04:00
oprofile [S390] irq: external interrupt code passing 2012-03-11 11:59:29 -04:00
defconfig [S390] defconfig: switch on CONFIG_DEVTMPFS 2011-10-30 15:16:42 +01:00
Kbuild [S390] make arch/s390 subdirectories depend on config option 2011-12-27 11:27:12 +01:00
Kconfig [S390] KEYS: Enable the compat keyctl wrapper on s390x 2012-02-24 18:01:36 +01:00
Kconfig.debug [S390] Write protect module text and RO data 2011-03-15 17:08:23 +01:00
Makefile [S390] cleanup entry point definition 2012-01-18 18:03:41 +01:00