Re: [PATCH bpf-next 3/3] bpf, arm64: use bpf_jit_binary_pack_alloc

[Puranjay Mohan]

Hi,

On Mon, Jun 5, 2023 at 7:05 PM Song Liu <song@xxxxxxxxxx> wrote:
>
> On Mon, Jun 5, 2023 at 12:40 AM Puranjay Mohan <puranjay12@xxxxxxxxx> wrote:
> >
> > Use bpf_jit_binary_pack_alloc for memory management of JIT binaries in
> > ARM64 BPF JIT. The bpf_jit_binary_pack_alloc creates a pair of RW and RX
> > buffers. The JIT writes the program into the RW buffer. When the JIT is
> > done, the program is copied to the final ROX buffer
> > with bpf_jit_binary_pack_finalize.
> >
> > Implement bpf_arch_text_copy() and bpf_arch_text_invalidate() for ARM64
> > JIT as these functions are required by bpf_jit_binary_pack allocator.
> >
> > Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>
> > ---
> >  arch/arm64/net/bpf_jit_comp.c | 119 +++++++++++++++++++++++++++++-----
> >  1 file changed, 102 insertions(+), 17 deletions(-)
> >
> > diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> > index 145b540ec34f..ee9414cadea8 100644
> > --- a/arch/arm64/net/bpf_jit_comp.c
> > +++ b/arch/arm64/net/bpf_jit_comp.c
> > @@ -76,6 +76,7 @@ struct jit_ctx {
> >         int *offset;
> >         int exentry_idx;
> >         __le32 *image;
> > +       __le32 *ro_image;
>
> We are using:
> image vs. ro_image
> rw_header vs. header
> rw_image_ptr vs. image_ptr

Will use "rw_image" and "image" in the next version.

>
> Shall we be more consistent with rw_ or ro_ prefix?
>
> >         u32 stack_size;
> >         int fpb_offset;
> >  };
> > @@ -205,6 +206,20 @@ static void jit_fill_hole(void *area, unsigned int size)
> >                 *ptr++ = cpu_to_le32(AARCH64_BREAK_FAULT);
> >  }
> >
> > +int bpf_arch_text_invalidate(void *dst, size_t len)
> > +{
> > +       __le32 *ptr;
> > +       int ret;
> > +
> > +       for (ptr = dst; len >= sizeof(u32); len -= sizeof(u32)) {
> > +               ret = aarch64_insn_patch_text_nosync(ptr++, AARCH64_BREAK_FAULT);
>
> I think one aarch64_insn_patch_text_nosync() per 4 byte is too much overhead.
> Shall we add a helper to do this in bigger patches?

What would be the most efficient way to build this helper? As arm64 doesn't
have the __text_poke() API. Calling copy_to_kernel_nofault() in a loop might
not be the best way. One way would be to use __put_kernel_nofault() directly.

Also, what should we call this helper? aarch64_insn_memset() ?

Thanks,
Puranjay