On 7/8/2021 5:52 AM, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:

Hi Anthony and Steven,

在 2020/7/28 1:11, Anthony Yznaga 写道:

quoted

This patchset adds support for preserving an anonymous memory range across
exec(3) using a new madvise MADV_DOEXEC argument.  The primary benefit for
sharing memory in this manner, as opposed to re-attaching to a named shared
memory segment, is to ensure it is mapped at the same virtual address in
the new process as it was in the old one.  An intended use for this is to
preserve guest memory for guests using vfio while qemu exec's an updated
version of itself.  By ensuring the memory is preserved at a fixed address,
vfio mappings and their associated kernel data structures can remain valid.
In addition, for the qemu use case, qemu instances that back guest RAM with
anonymous memory can be updated.

We have a requirement like yours, but ours seems more complex. We want to
isolate some memory regions from the VM's memory space and the start a child
process who will using these memory regions.

I've wrote a draft to support this feature, but I just find that my draft is
pretty like yours.

It seems that you've already abandoned this patchset, why ?

Hi Longpeng,
  The reviewers did not like the proposal for several reasons, but the showstopper
was that they did not want to add complexity to the exec path in the kernel.  You
can read the email archive for details.

We solved part of our problem by adding new vfio interfaces: VFIO_DMA_UNMAP_FLAG_VADDR
and VFIO_DMA_MAP_FLAG_VADDR.  That solves the vfio problem for shared memory, but not
for mmap MAP_ANON memory.

- Steve

quoted

Patches 1 and 2 ensure that loading of ELF load segments does not silently
clobber existing VMAS, and remove assumptions that the stack is the only
VMA in the mm when the stack is set up.  Patch 1 re-introduces the use of
MAP_FIXED_NOREPLACE to load ELF binaries that addresses the previous issues
and could be considered on its own.

Patches 3, 4, and 5 introduce the feature and an opt-in method for its use
using an ELF note.

Anthony Yznaga (5):
  elf: reintroduce using MAP_FIXED_NOREPLACE for elf executable mappings
  mm: do not assume only the stack vma exists in setup_arg_pages()
  mm: introduce VM_EXEC_KEEP
  exec, elf: require opt-in for accepting preserved mem
  mm: introduce MADV_DOEXEC

 arch/x86/Kconfig                       |   1 +
 fs/binfmt_elf.c                        | 196 +++++++++++++++++++++++++--------
 fs/exec.c                              |  33 +++++-
 include/linux/binfmts.h                |   7 +-
 include/linux/mm.h                     |   5 +
 include/uapi/asm-generic/mman-common.h |   3 +
 kernel/fork.c                          |   2 +-
 mm/madvise.c                           |  25 +++++
 mm/mmap.c                              |  47 ++++++++
 9 files changed, 266 insertions(+), 53 deletions(-)