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

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Date:   Tue, 11 Jan 2022 17:26:55 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v3 bpf-next 7/7] bpf, x86_64: use bpf_prog_pack allocator



> On Jan 11, 2022, at 4:04 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> 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.

Aha, I didn't realize the file is about 50:50 with the two styles. I can 
change it in v4. 

Thanks,
Song