Re: [RFC PATCH 0/5] madvise MADV_DOEXEC

Kirill Tkhai
2020-07-28T12:26:30Z

On 27.07.2020 20:11, Anthony Yznaga wrote:
> 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,

So, the goal is an update of QEMU binary without a stopping of virtual machine?

> 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.
>
> 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(-)
>