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From: KP Singh <kpsingh@kernel.org>
To: Jie Meng <jmeng@fb.com>
Cc: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org,
	daniel@iogearbox.net
Subject: Re: [PATCH bpf-next] bpf,x64: Remove unnecessary check on existence of SSE2
Date: Tue, 4 Oct 2022 03:04:20 +0200	[thread overview]
Message-ID: <CACYkzJ7_ZNKsE5b9ECqf7+U9qs8E2hbx4GXvAhrnG3iVApqLjg@mail.gmail.com> (raw)
In-Reply-To: <20221003011727.1192900-1-jmeng@fb.com>

On Mon, Oct 3, 2022 at 3:17 AM Jie Meng <jmeng@fb.com> wrote:
>
> SSE2 and hence lfence are architectural in x86-64 and no need to check
> whether they're supported in CPU.

Why do you say this?

The Instruction set reference does mention that:

Exceptions:

#UD If CPUID.01H:EDX.SSE2[bit 26] = 0

(undefined instruction when the CPUID.SSE2 bit is unset)

and also that the CPUID feature flag is SSE2

>
> Signed-off-by: Jie Meng <jmeng@fb.com>
> ---
>  arch/x86/net/bpf_jit_comp.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index d09c54f3d2e0..b2124521305e 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -1289,8 +1289,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
>
>                         /* speculation barrier */
>                 case BPF_ST | BPF_NOSPEC:
> -                       if (boot_cpu_has(X86_FEATURE_XMM2))
> -                               EMIT_LFENCE();
> +                       EMIT_LFENCE();
>                         break;
>
>                         /* ST: *(u8*)(dst_reg + off) = imm */
> --
> 2.30.2
>

  reply	other threads:[~2022-10-04  1:05 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-03  1:17 [PATCH bpf-next] bpf,x64: Remove unnecessary check on existence of SSE2 Jie Meng
2022-10-04  1:04 ` KP Singh [this message]
2022-10-04  3:50   ` Jie Meng
2022-10-05  0:30     ` KP Singh
2022-10-05 17:00       ` [PATCH bpf-next v2] " Jie Meng
2022-10-06  0:58         ` KP Singh
2022-10-07 14:30         ` patchwork-bot+netdevbpf

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