linux-kernel - Re: [PATCH v2 14/14] bpf,x86: Respect X86_FEATURE

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Message-ID: <20211021223719.GY174703@worktop.programming.kicks-ass.net>
Date:   Fri, 22 Oct 2021 00:37:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     X86 ML <x86@...nel.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH v2 14/14] bpf,x86: Respect X86_FEATURE_RETPOLINE*

On Thu, Oct 21, 2021 at 11:03:33AM -0700, Alexei Starovoitov wrote:

> > I nicked it from emit_bpf_tail_call() in the 32bit jit :-) It seemed a
> > lot more robust than the 64bit one and I couldn't figure out why the
> > difference.
> 
> Interesting. Daniel will recognize that trick then :)

> > Is there concurrency on the jit?
> 
> The JIT of different progs can happen in parallel.

In that case I don't think the patch is safe. I'll see if I can find a
variant that doesn't use static storage.