linux-kernel - Re: [GIT PULL] Final KVM fix for Linux 6.7

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Message-ID: <CAHk-=wjc5x_Y=MX35vaoWodpfOU86_gm6BQTGWXgDeFMPneTrQ@mail.gmail.com>
Date: Fri, 5 Jan 2024 09:38:22 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	peterz@...radead.org, paulmck@...nel.org
Subject: Re: [GIT PULL] Final KVM fix for Linux 6.7

On Fri, 5 Jan 2024 at 09:29, Sean Christopherson <seanjc@...gle.com> wrote:
>
> Ha!  That's what I suggested too, clearly Paolo is the weird one :-)

Well, it's technically one fewer operation to do it our way, but
Paolo's version is

 (a) textually one character shorter

 (b) something the compiler can (and likely will) munge anyway, since
boolean operation optimizations are common

 (c) with the 'andn' instruction, the "fewer operations" isn't
necessarily fewer instructions

Of course, we can't currently use 'andn' in kernel code due to it
being much too new and requires BMI1. Plus the memory op version is
the wrong way around (ie the "not" part of the op only works on
register inputs), but _evenbtually_ that might have been an argument.

            Linus