From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de,
linux-kernel@vger.kernel.org, x86@kernel.org,
kvm@vger.kernel.org, jthoughton@google.com
Subject: Re: [PATCH v2 12/12] x86/kvm/emulate: Avoid RET for fastops
Date: Sat, 16 Nov 2024 10:39:54 +0100 [thread overview]
Message-ID: <20241116093954.GL22801@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20241115184104.pud5l26v5vx3vcbp@jpoimboe>
On Fri, Nov 15, 2024 at 10:41:04AM -0800, Josh Poimboeuf wrote:
> On Mon, Nov 11, 2024 at 12:59:47PM +0100, Peter Zijlstra wrote:
> > Since there is only a single fastop() function, convert the FASTOP
> > stuff from CALL_NOSPEC+RET to JMP_NOSPEC+JMP, avoiding the return
> > thunks and all that jazz.
> >
> > Specifically FASTOPs rely on the return thunk to preserve EFLAGS,
> > which not all of them can trivially do (call depth tracing suffers
> > here).
> >
> > Objtool strenuously complains about this:
> >
> > - indirect call without a .rodata, fails to determine JUMP_TABLE,
> > annotate
> > - fastop functions fall through, exception
> > - unreachable instruction after fastop_return, save/restore
>
> This wording makes it sound like this patch triggers objtool warnings,
> which I'm guessing is not true?
Right, no, it did without the fixups. This was a (poorly worder) attempt
at explaining the reasons for the various annotations in the patch.
next prev parent reply other threads:[~2024-11-16 9:39 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-11 11:59 [PATCH v2 00/12] x86/kvm/emulate: Avoid RET for FASTOPs Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 01/12] objtool: Generic annotation infrastructure Peter Zijlstra
2024-11-15 18:38 ` Josh Poimboeuf
2024-11-16 9:33 ` Peter Zijlstra
2024-11-20 0:31 ` Josh Poimboeuf
2024-11-20 1:04 ` Josh Poimboeuf
2024-11-20 8:52 ` Peter Zijlstra
2024-11-20 16:03 ` Josh Poimboeuf
2024-11-20 16:03 ` Josh Poimboeuf
2024-11-21 11:46 ` Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 02/12] objtool: Convert ANNOTATE_NOENDBR to ANNOTATE Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 03/12] objtool: Convert ANNOTATE_RETPOLINE_SAFE " Peter Zijlstra
2024-11-15 18:39 ` Josh Poimboeuf
2024-11-16 9:34 ` Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 04/12] objtool: Convert instrumentation_{begin,end}() " Peter Zijlstra
2024-11-15 18:40 ` Josh Poimboeuf
2024-11-16 9:36 ` Peter Zijlstra
2024-11-16 9:51 ` Peter Zijlstra
2024-11-16 10:06 ` Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 05/12] objtool: Convert VALIDATE_UNRET_BEGIN " Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 06/12] objtool: Convert ANNOTATE_IGNORE_ALTERNATIVE " Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 07/12] objtool: Convert ANNOTATE_INTRA_FUNCTION_CALLS " Peter Zijlstra
2024-11-15 18:40 ` Josh Poimboeuf
2024-11-16 9:37 ` Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 08/12] objtool: Collapse annotate sequences Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 09/12] x86/nospec: JMP_NOSPEC Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 10/12] x86,nospec: Simplify {JMP,CALL}_NOSPEC (part 2) Peter Zijlstra
2024-11-15 18:40 ` Josh Poimboeuf
2024-11-16 9:39 ` Peter Zijlstra
2024-11-11 11:59 ` [PATCH v2 11/12] x86/kvm/emulate: Implement test_cc() in C Peter Zijlstra
2024-11-11 17:13 ` Sean Christopherson
2024-11-11 11:59 ` [PATCH v2 12/12] x86/kvm/emulate: Avoid RET for fastops Peter Zijlstra
2024-11-11 16:27 ` Peter Zijlstra
2024-11-11 17:26 ` Sean Christopherson
2024-11-11 18:28 ` Peter Zijlstra
2024-11-15 18:41 ` Josh Poimboeuf
2024-11-16 9:39 ` Peter Zijlstra [this message]
2024-11-11 17:27 ` [PATCH v2 00/12] x86/kvm/emulate: Avoid RET for FASTOPs Sean Christopherson
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