linux-kernel - Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND

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Date:   Mon, 9 Mar 2020 21:22:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>, stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS

On Mon, Mar 09, 2020 at 08:05:18PM +0100, Thomas Gleixner wrote:
> Andy Lutomirski <luto@...nel.org> writes:

> > I'm okay with the save/restore dance, I guess.  It's just yet more
> > entry crud to deal with architecture nastiness, except that this
> > nastiness is 100% software and isn't Intel/AMD's fault.
> 
> And we can do it in C and don't have to fiddle with it in the ASM
> maze.

Right; I'd still love to kill KVM_ASYNC_PF_SEND_ALWAYS though, even if
we do the save/restore in do_nmi(). That is some wild brain melt. Also,
AFAIK none of the distros are actually shipping a PREEMPT=y kernel
anyway, so killing it shouldn't matter much.

If people want to recover that, I'd suggest they sit down and create a
sane paravirt interface for this.