From: Peter Zijlstra <peterz@infradead.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: x86@kernel.org, jpoimboe@redhat.com, andrew.cooper3@citrix.com,
linux-kernel@vger.kernel.org, ndesaulniers@google.com,
daniel@iogearbox.net, bpf@vger.kernel.org, andrii@kernel.org
Subject: Re: [PATCH v2 14/14] bpf,x86: Respect X86_FEATURE_RETPOLINE*
Date: Thu, 21 Oct 2021 10:47:00 +0200 [thread overview]
Message-ID: <YXEpBKxUICIPVj14@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20211021000502.ltn5o6ji6offwzeg@ast-mbp.dhcp.thefacebook.com>
On Wed, Oct 20, 2021 at 05:05:02PM -0700, Alexei Starovoitov wrote:
> On Wed, Oct 20, 2021 at 01:09:51PM +0200, Peter Zijlstra wrote:
> > @@ -446,25 +440,8 @@ static void emit_bpf_tail_call_indirect(
> > {
> > int tcc_off = -4 - round_up(stack_depth, 8);
> > u8 *prog = *pprog, *start = *pprog;
> > - int pop_bytes = 0;
> > - int off1 = 42;
> > - int off2 = 31;
> > - int off3 = 9;
> > -
> > - /* count the additional bytes used for popping callee regs from stack
> > - * that need to be taken into account for each of the offsets that
> > - * are used for bailing out of the tail call
> > - */
> > - pop_bytes = get_pop_bytes(callee_regs_used);
> > - off1 += pop_bytes;
> > - off2 += pop_bytes;
> > - off3 += pop_bytes;
> > -
> > - if (stack_depth) {
> > - off1 += 7;
> > - off2 += 7;
> > - off3 += 7;
> > - }
> > + static int out_label = -1;
>
> Interesting idea!
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.
> All insn emits trying to do the right thing from the start.
> Here the logic assumes that there will be at least two passes over image.
> I think that is correct, but we never had such assumption.
That's not exactly true; I think image is NULL on every first run, so
all insn that depend on it will be wrong to start with. Equally there's
a number of insn that seem to depend on addrs[i], that also requires at
least two passes.
> A comment is certainly must have.
I can certainly add one, although I think we'll disagree on the comment
style :-)
> The race is possible too. Not sure whether READ_ONCE/WRITE_ONCE
> are really warranted though. Might be overkill.
Is there concurrency on the jit?
> Once you have a git branch with all the changes I can give it a go.
Ok, I'll go polish this thing and stick it in the tree mentioned in the
cover letter.
> Also you can rely on our BPF CI.
> Just cc your patchset to bpf@vger and add [PATCH bpf-next] to a subject.
> In patchwork there will be "bpf/vmtest-bpf-next" link that
> builds kernel, selftests and runs everything.
What's a patchwork and where do I find it?
> It's pretty much the same as selftests/bpf/vmtest.sh, but with the latest
> clang nightly and other deps like pahole.
nice.
next prev parent reply other threads:[~2021-10-21 8:47 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 [this message]
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
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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