From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Puranjay Mohan <puranjay12@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
bpf <bpf@vger.kernel.org>, KP Singh <kpsingh@kernel.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf-next v3 3/3] bpf, arm64: use bpf_jit_binary_pack_alloc
Date: Wed, 21 Jun 2023 09:24:54 -0700 [thread overview]
Message-ID: <CAADnVQJqDOMABEx8JuU6r_Dehyf=SkDfRNChx1oNfqPoo7pSrw@mail.gmail.com> (raw)
In-Reply-To: <ZJMXqTffB22LSOkd@FVFF77S0Q05N>
On Wed, Jun 21, 2023 at 8:31 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Mon, Jun 19, 2023 at 10:01:21AM +0000, Puranjay Mohan 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 RX 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@gmail.com>
>
> From a quick look, I don't beleive the I-cache maintenance is quite right --
> explanation below.
>
> > @@ -1562,34 +1610,39 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
> >
> > /* 3. Extra pass to validate JITed code. */
> > if (validate_ctx(&ctx)) {
> > - bpf_jit_binary_free(header);
> > prog = orig_prog;
> > - goto out_off;
> > + goto out_free_hdr;
> > }
> >
> > /* And we're done. */
> > if (bpf_jit_enable > 1)
> > bpf_jit_dump(prog->len, prog_size, 2, ctx.image);
> >
> > - bpf_flush_icache(header, ctx.image + ctx.idx);
> > + bpf_flush_icache(ro_header, ctx.ro_image + ctx.idx);
>
> I think this is too early; we haven't copied the instructions into the
> ro_header yet, so that still contains stale instructions.
>
> IIUC at the whole point of this is to pack multiple programs into shared ROX
> pages, and so there can be an executable mapping of the RO page at this point,
> and the CPU can fetch stale instructions throught that.
>
> Note that *regardless* of whether there is an executeable mapping at this point
> (and even if no executable mapping exists until after the copy), we at least
> need a data cache clean to the PoU *after* the copy (so fetches don't get a
> stale value from the PoU), and the I-cache maintenance has to happeon the VA
> the instrutions will be executed from (or VIPT I-caches can still contain stale
> instructions).
Good catch.
Also considering the boot issue reported in the other thread
I removed this series from bpf-next.
Looks like another respin is necessary.
next prev parent reply other threads:[~2023-06-21 16:25 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-19 10:01 [PATCH bpf-next v3 0/3] bpf, arm64: use BPF prog pack allocator in BPF JIT Puranjay Mohan
2023-06-19 10:01 ` [PATCH bpf-next v3 1/3] bpf: make bpf_prog_pack allocator portable Puranjay Mohan
2023-06-19 10:01 ` [PATCH bpf-next v3 2/3] arm64: patching: Add aarch64_insn_copy() Puranjay Mohan
2023-06-19 10:01 ` [PATCH bpf-next v3 3/3] bpf, arm64: use bpf_jit_binary_pack_alloc Puranjay Mohan
2023-06-20 23:24 ` Song Liu
2023-06-21 15:31 ` Mark Rutland
2023-06-21 16:24 ` Alexei Starovoitov [this message]
2023-06-21 20:57 ` Puranjay Mohan
2023-06-22 8:23 ` Mark Rutland
2023-06-22 8:47 ` Puranjay Mohan
2023-06-22 9:36 ` Mark Rutland
2023-06-20 23:40 ` [PATCH bpf-next v3 0/3] bpf, arm64: use BPF prog pack allocator in BPF JIT patchwork-bot+netdevbpf
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