Re: [RFC PATCH 0/5] madvise MADV_DOEXEC

Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-07-08T09:52:24Z

Hi Anthony and Steven,

在 2020/7/28 1:11, Anthony Yznaga 写道:
> 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 ?

> 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(-)
>

--
Sincerely yours,
Longpeng(Mike)