Re: [PATCH bpf-next v2 0/5] execmem_alloc for BPF programs

[Song Liu <song@kernel.org>]

On Mon, Nov 7, 2022 at 2:41 PM Song Liu <song@kernel.org> wrote:
>

[...]

>
>
> This set enables bpf programs and bpf dispatchers to share huge pages with
> new API:
>   execmem_alloc()
>   execmem_alloc()
>   execmem_fill()
>
> The idea is similar to Peter's suggestion in [1].
>
> execmem_alloc() manages a set of PMD_SIZE RO+X memory, and allocates these
> memory to its users. execmem_alloc() is used to free memory allocated by
> execmem_alloc(). execmem_fill() is used to update memory allocated by
> execmem_alloc().

Sigh, I just realized this thread made through linux-mm@kvack.org, but got
dropped by bpf@vger.kernel.org, so I guess I will have to resend v3.

Currently, I have got the following action items for v3:
1. Add unify API to allocate text memory to motivation;
2. Update Documentation/x86/x86_64/mm.rst;
3. Allow none PMD_SIZE allocation for powerpc.

1 and 2 are relatively simple. We can probably do 3 in a follow up patch
(as I don't have powerpc environments for testing). Did I miss anything?

Besides these, does this set look reasonable? Andrew and Peter, could
you please share your comments on this?

Thanks,
Song

>
> Memory allocated by execmem_alloc() is RO+X, so this doesnot violate W^X.
> The caller has to update the content with text_poke like mechanism.
> Specifically, execmem_fill() is provided to update memory allocated by
> execmem_alloc(). execmem_fill() also makes sure the update stays in the
> boundary of one chunk allocated by execmem_alloc(). Please refer to patch
> 1/5 for more details of
>
> Patch 3/5 uses these new APIs in bpf program and bpf dispatcher.
>
> Patch 4/5 and 5/5 allows static kernel text (_stext to _etext) to share
> PMD_SIZE pages with dynamic kernel text on x86_64. This is achieved by
> allocating PMD_SIZE pages to roundup(_etext, PMD_SIZE), and then use
> _etext to roundup(_etext, PMD_SIZE) for dynamic kernel text.
>
> [1] https://lore.kernel.org/bpf/Ys6cWUMHO8XwyYgr@hirez.programming.kicks-ass.net/
> [2] RFC v1: https://lore.kernel.org/linux-mm/20220818224218.2399791-3-song@kernel.org/T/
> [3] v1: https://lore.kernel.org/bpf/20221031222541.1773452-1-song@kernel.org/
> [4] https://lore.kernel.org/bpf/Y2ioTodn+mBXdIqp@ziqianlu-desk2/
> [5] https://lore.kernel.org/bpf/20220707223546.4124919-1-song@kernel.org/
>
> Changes PATCH v1 => v2:
> 1. Rename the APIs as execmem_* (Christoph Hellwig)
> 2. Add more information about the motivation of this work (and follow up
>    works in for kernel modules, various trampolines, etc).
>    (Luis Chamberlain, Rick Edgecombe, Mike Rapoport, Aaron Lu)
> 3. Include expermential results from previous bpf_prog_pack and the
>    community. (Aaron Lu, Luis Chamberlain, Rick Edgecombe)
>
> Changes RFC v2 => PATCH v1:
> 1. Add vcopy_exec(), which updates memory allocated by vmalloc_exec(). It
>    also ensures vcopy_exec() is only used to update memory from one single
>    vmalloc_exec() call. (Christoph Hellwig)
> 2. Add arch_vcopy_exec() and arch_invalidate_exec() as wrapper for the
>    text_poke() like logic.
> 3. Drop changes for kernel modules and focus on BPF side changes.
>
> Changes RFC v1 => RFC v2:
> 1. Major rewrite of the logic of vmalloc_exec and vfree_exec. They now
>    work fine with BPF programs (patch 1, 2, 4). But module side (patch 3)
>    still need some work.
>
> Song Liu (5):
>   vmalloc: introduce execmem_alloc, execmem_free, and execmem_fill
>   x86/alternative: support execmem_alloc() and execmem_free()
>   bpf: use execmem_alloc for bpf program and bpf dispatcher
>   vmalloc: introduce register_text_tail_vm()
>   x86: use register_text_tail_vm
>
>  arch/x86/include/asm/pgtable_64_types.h |   1 +
>  arch/x86/kernel/alternative.c           |  12 +
>  arch/x86/mm/init_64.c                   |   4 +-
>  arch/x86/net/bpf_jit_comp.c             |  23 +-
>  include/linux/bpf.h                     |   3 -
>  include/linux/filter.h                  |   5 -
>  include/linux/vmalloc.h                 |   9 +
>  kernel/bpf/core.c                       | 180 +-----------
>  kernel/bpf/dispatcher.c                 |  11 +-
>  mm/nommu.c                              |  12 +
>  mm/vmalloc.c                            | 354 ++++++++++++++++++++++++
>  11 files changed, 412 insertions(+), 202 deletions(-)
>
> --
> 2.30.2