linux-kernel - Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls in _

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Message-ID: <20250502110817.GX4198@noisy.programming.kicks-ass.net>
Date: Fri, 2 May 2025 13:08:17 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: x86@...nel.org, kys@...rosoft.com, haiyangz@...rosoft.com,
	wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	hpa@...or.com, seanjc@...gle.com, ardb@...nel.org, kees@...nel.org,
	Arnd Bergmann <arnd@...db.de>, gregkh@...uxfoundation.org,
	jpoimboe@...nel.org, linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-efi@...r.kernel.org, samitolvanen@...gle.com,
	ojeda@...nel.org
Subject: Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls
 in __nocfi functions

On Thu, May 01, 2025 at 08:33:57PM +0200, Paolo Bonzini wrote:
> On Wed, Apr 30, 2025 at 1:26 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > Notably the KVM fastop emulation stuff -- which I've completely rewritten for
> > this version -- the generated code doesn't look horrific, but is slightly more
> > verbose. I'm running on the assumption that instruction emulation is not super
> > performance critical these days of zero VM-exit VMs etc.
> 
> It's definitely going to be slower, but I guess it's okay these days.

Yeah, it adds a bunch of branches at the very least. But that was indeed
the argument, we shouldn't care much these days.

> It's really only somewhat hot with really old processors
> (pre-Westmere) and only when running big real mode code.

Right, really old stuff :-)