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authorJason Baron <jbaron@redhat.com>2012-03-23 18:02:51 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-23 19:58:42 -0400
commit909af768e88867016f427264ae39d27a57b6a8ed (patch)
tree5068b4d98e4bedecde89d9113dc7ef8c69633f45 /arch/tile
parent1cc684ab75123efe7ff446eb821d44375ba8fa30 (diff)
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>
Diffstat (limited to 'arch/tile')
-rw-r--r--arch/tile/mm/elf.c8
1 files changed, 1 insertions, 7 deletions
diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
index 55e58e93bfc5..1a00fb64fc88 100644
--- a/arch/tile/mm/elf.c
+++ b/arch/tile/mm/elf.c
@@ -117,17 +117,11 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
117 117
118 /* 118 /*
119 * MAYWRITE to allow gdb to COW and set breakpoints 119 * MAYWRITE to allow gdb to COW and set breakpoints
120 *
121 * Make sure the vDSO gets into every core dump. Dumping its
122 * contents makes post-mortem fully interpretable later
123 * without matching up the same kernel and hardware config to
124 * see what PC values meant.
125 */ 120 */
126 vdso_base = VDSO_BASE; 121 vdso_base = VDSO_BASE;
127 retval = install_special_mapping(mm, vdso_base, PAGE_SIZE, 122 retval = install_special_mapping(mm, vdso_base, PAGE_SIZE,
128 VM_READ|VM_EXEC| 123 VM_READ|VM_EXEC|
129 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC| 124 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
130 VM_ALWAYSDUMP,
131 vdso_pages); 125 vdso_pages);
132 126
133#ifndef __tilegx__ 127#ifndef __tilegx__