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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>
Subject: Re: [PATCH v2 14/14] bpf,x86: Respect X86_FEATURE_RETPOLINE*
Date: Thu, 21 Oct 2021 16:42:12 -0700	[thread overview]
Message-ID: <CAADnVQ+iMysKSKBGzx7Wa+ygpr9nTJbRo4eGYADLFDE4PmtjOQ@mail.gmail.com> (raw)
In-Reply-To: <20211021233852.gbkyl7wpunyyq4y5@treble>

On Thu, Oct 21, 2021 at 4:38 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Thu, Oct 21, 2021 at 04:24:33PM -0700, Alexei Starovoitov wrote:
> > On Thu, Oct 21, 2021 at 3:40 PM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > 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.
> >
> > The variable can only change from one fixed value to another fixed value.
> > Different threads will compute the same value. So I think it's safe
> > as-is. READ_ONCE/WRITE_ONCE won't hurt though.
>
> But the size of the generated code differs based on the
> emit_bpf_tail_call_indirect() args: 'callee_regs_used' and
> 'stack_depth'.  So the fixed value can change.

Ahh. Right. It's potentially a different offset for every prog.
Let's put it into struct jit_context then.

  reply	other threads:[~2021-10-21 23:42 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-20 10:44 [PATCH v2 00/14] x86: Rewrite the retpoline rewrite logic Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 01/14] objtool: Tag retpoline thunk symbols Peter Zijlstra
2021-10-20 15:17   ` Josh Poimboeuf
2021-10-26  7:55     ` Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 02/14] objtool: Explicitly avoid self modifying code in .altinstr_replacement Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 03/14] objtool: Shrink struct instruction Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 04/14] objtool,x86: Replace alternatives with .retpoline_sites Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 05/14] x86/retpoline: Remove unused replacement symbols Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 06/14] x86/asm: Fix register order Peter Zijlstra
2021-10-22 19:27   ` David Laight
2021-10-25 14:09   ` Borislav Petkov
2021-10-20 10:44 ` [PATCH v2 07/14] x86/asm: Fixup odd GEN-for-each-reg.h usage Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 08/14] x86/retpoline: Create a retpoline thunk array Peter Zijlstra
2021-10-20 15:57   ` Josh Poimboeuf
2021-10-20 16:46     ` Andrew Cooper
2021-10-20 17:09       ` Josh Poimboeuf
2021-10-20 19:22         ` Peter Zijlstra
2021-10-20 19:43           ` Josh Poimboeuf
2021-10-20 19:34       ` Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 09/14] x86/alternative: Implement .retpoline_sites support Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 10/14] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 11/14] x86/alternative: Try inline spectre_v2=retpoline,amd Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 12/14] x86/alternative: Add debug prints to apply_retpolines() Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 13/14] x86,bugs: Unconditionally allow spectre_v2=retpoline,amd Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 14/14] bpf,x86: Respect X86_FEATURE_RETPOLINE* Peter Zijlstra
2021-10-20 11:09   ` Peter Zijlstra
2021-10-20 16:56     ` Josh Poimboeuf
2021-10-20 19:23       ` Peter Zijlstra
2021-10-21  0:05     ` Alexei Starovoitov
2021-10-21  8:47       ` Peter Zijlstra
2021-10-21 18:03         ` Alexei Starovoitov
2021-10-21 22:37           ` Peter Zijlstra
2021-10-21 23:24             ` Alexei Starovoitov
2021-10-21 23:38               ` Josh Poimboeuf
2021-10-21 23:42                 ` Alexei Starovoitov [this message]
2021-10-22 11:31                   ` Peter Zijlstra
2021-10-22 15:22                     ` Alexei Starovoitov
2021-10-25 13:44                       ` Maciej Fijalkowski
2021-10-25 12:42                         ` Peter Zijlstra
2021-10-21 23:51         ` Zvi Effron
2021-10-22  8:33           ` Peter Zijlstra
2021-10-22 21:06             ` Zvi Effron
2021-10-21  0:07   ` Alexei Starovoitov
2021-10-21  0:18     ` Josh Poimboeuf
2021-10-21  8:53       ` Peter Zijlstra

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