linux-kernel - Re: [PATCH v3 bpf-next 7/7] bpf, x86_64: use bpf_prog

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Message-ID: <Yd1yPATp1viijqbi@hirez.programming.kicks-ass.net>
Date:   Tue, 11 Jan 2022 13:04:12 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <song@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kernel-team@...com, x86@...nel.org,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH v3 bpf-next 7/7] bpf, x86_64: use bpf_prog_pack allocator

On Wed, Jan 05, 2022 at 06:25:33PM -0800, Song Liu wrote:
> From: Song Liu <songliubraving@...com>
> 
> Use bpf_prog_pack allocator in x86_64 jit.
> 
> The program header from bpf_prog_pack is read only during the jit process.
> Therefore, the binary is first written to a temporary buffer, and later
> copied to final location with text_poke_jit().
> 
> Similarly, jit_fill_hole() is updated to fill the hole with 0xcc using
> text_poke_jit().
> 
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  arch/x86/net/bpf_jit_comp.c | 131 +++++++++++++++++++++++++++---------
>  1 file changed, 100 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index fe4f08e25a1d..ad69a64ee4fe 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -216,11 +216,33 @@ static u8 simple_alu_opcodes[] = {
>  	[BPF_ARSH] = 0xF8,
>  };
>  
> +static char jit_hole_buffer[PAGE_SIZE] = {};
> +
>  static void jit_fill_hole(void *area, unsigned int size)
> +{
> +	struct bpf_binary_header *hdr = area;
> +	int i;
> +
> +	for (i = 0; i < roundup(size, PAGE_SIZE); i += PAGE_SIZE) {
> +		int s;
> +
> +		s = min_t(int, PAGE_SIZE, size - i);
> +		text_poke_jit(area + i, jit_hole_buffer, s);
> +	}
> +
> +	/* bpf_jit_binary_alloc_pack cannot write size directly to the ro
> +	 * mapping. Write it here with text_poke_jit().
> +	 */

Could we move this file towards regular comment style please? It's
already mixed style, let's take the opportunity and not add more
net-style comments.

> +	text_poke_jit(&hdr->size, &size, sizeof(size));
> +}