linux-kernel - Re: [PATCH bpf-next 2/3] arm64: patching: Add aarch64_insn

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Date:   Mon, 5 Jun 2023 20:04:34 +0200
From:   Puranjay Mohan <puranjay12@...il.com>
To:     Song Liu <song@...nel.org>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, catalin.marinas@....com,
        mark.rutland@....com, bpf@...r.kernel.org, kpsingh@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/3] arm64: patching: Add aarch64_insn_copy()

On Mon, Jun 5, 2023 at 6:42 PM Song Liu <song@...nel.org> wrote:
>
> On Mon, Jun 5, 2023 at 12:40 AM Puranjay Mohan <puranjay12@...il.com> wrote:
> >
> > This will be used by BPF JIT compiler to dump JITed binary to a RX huge
> > page, and thus allow multiple BPF programs sharing the a huge (2MB)
> > page.
> >
> > The bpf_prog_pack allocator that implements the above feature allocates
> > a RX/RW buffer pair. The JITed code is written to the RW buffer and then
> > this function will be used to copy the code from RW to RX buffer.
> >
> > Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
>
> Acked-by: Song Liu <song@...nel.org>
>
> With a nit below.
>
> > ---
> >  arch/arm64/include/asm/patching.h |  1 +
> >  arch/arm64/kernel/patching.c      | 39 +++++++++++++++++++++++++++++++
> >  2 files changed, 40 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/patching.h b/arch/arm64/include/asm/patching.h
> > index 68908b82b168..dba9eb392bf1 100644
> > --- a/arch/arm64/include/asm/patching.h
> > +++ b/arch/arm64/include/asm/patching.h
> > @@ -8,6 +8,7 @@ int aarch64_insn_read(void *addr, u32 *insnp);
> >  int aarch64_insn_write(void *addr, u32 insn);
> >
> >  int aarch64_insn_write_literal_u64(void *addr, u64 val);
> > +void *aarch64_insn_copy(void *addr, const void *opcode, size_t len);
> >
> >  int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
> >  int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
> > diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
> > index b4835f6d594b..48c710f6a1ff 100644
> > --- a/arch/arm64/kernel/patching.c
> > +++ b/arch/arm64/kernel/patching.c
> > @@ -105,6 +105,45 @@ noinstr int aarch64_insn_write_literal_u64(void *addr, u64 val)
> >         return ret;
> >  }
> >
> > +/**
> > + * aarch64_insn_copy - Copy instructions into (an unused part of) RX memory
> > + * @addr: address to modify
> > + * @opcode: source of the copy
> > + * @len: length to copy
> > + *
> > + * Useful for JITs to dump new code blocks into unused regions of RX memory.
> > + */
>
> nit:
> I understand "addr" and "opcode" are used by x86 text_poke_copy(). But maybe
> we should call them "dst" and "src" or "to" and "from" or something similar?

Sure, I will call it "dst" and "src" in the next version.

Thanks,
Puranjay