linux-kernel - Re: [PATCH] KVM: X86: Fix async pf caused null-ptr-deref

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Date:   Tue, 30 Jun 2020 08:16:41 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Vivek Goyal <vgoyal@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: X86: Fix async pf caused null-ptr-deref

On Mon, 29 Jun 2020 at 23:42, Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> On Mon, Jun 29, 2020 at 03:59:25PM +0200, Paolo Bonzini wrote:
> > On 29/06/20 15:46, Vitaly Kuznetsov wrote:
> > >> +  if (!lapic_in_kernel(vcpu))
> > >> +          return 1;
> > >> +
> > > I'm not sure how much we care about !lapic_in_kernel() case but this
> > > change should be accompanied with userspace changes to not expose
> > > KVM_FEATURE_ASYNC_PF_INT or how would the guest know that writing a
> > > legitimate value will result in #GP?
> >
> > Almost any pv feature is broken with QEMU if kernel_irqchip=off.  I
> > wouldn't bother and I am seriously thinking of dropping all support for
> > that, including:
>
> Heh, based on my limited testing, that could be "Almost everything is
> broken with Qemu if kernel_irqchip=off".

It is broken for several years. :)