linux-kernel - Re: [RFC PATCH 0/5] madvise MADV

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Date:   Thu, 8 Jul 2021 17:52:16 +0800
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>
To:     Anthony Yznaga <anthony.yznaga@...cle.com>,
        <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-arch@...r.kernel.org>
CC:     <mhocko@...nel.org>, <tglx@...utronix.de>, <mingo@...hat.com>,
        <bp@...en8.de>, <x86@...nel.org>, <hpa@...or.com>,
        <viro@...iv.linux.org.uk>, <akpm@...ux-foundation.org>,
        <arnd@...db.de>, <ebiederm@...ssion.com>, <keescook@...omium.org>,
        <gerg@...ux-m68k.org>, <ktkhai@...tuozzo.com>,
        <christian.brauner@...ntu.com>, <peterz@...radead.org>,
        <esyr@...hat.com>, <jgg@...pe.ca>, <christian@...lner.me>,
        <areber@...hat.com>, <cyphar@...har.com>,
        <steven.sistare@...cle.com>,
        "Gonglei (Arei)" <arei.gonglei@...wei.com>
Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC

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)