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Date: Fri, 11 Sep 2020 19:25:33 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org Cc: Sean Christopherson <sean.j.christopherson@...el.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, "Dr . David Alan Gilbert" <dgilbert@...hat.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN On 11/09/20 11:31, Vitaly Kuznetsov wrote: > Even without in-kernel LAPIC we should allow writing '0' to > MSR_KVM_ASYNC_PF_EN as we're not enabling the mechanism. In > particular, QEMU with 'kernel-irqchip=off' fails to start > a guest with > > qemu-system-x86_64: error: failed to set MSR 0x4b564d02 to 0x0 > > Fixes: 9d3c447c72fb2 ("KVM: X86: Fix async pf caused null-ptr-deref") > Reported-by: Dr. David Alan Gilbert <dgilbert@...hat.com> > Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com> > --- > arch/x86/kvm/x86.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index d39d6cf1d473..44a86f7f2397 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2730,9 +2730,6 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data) > if (data & 0x30) > return 1; > > - if (!lapic_in_kernel(vcpu)) > - return 1; > - > vcpu->arch.apf.msr_en_val = data; > > if (!kvm_pv_async_pf_enabled(vcpu)) { > @@ -2741,6 +2738,9 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data) > return 0; > } > > + if (!lapic_in_kernel(vcpu)) > + return 1; > + > if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa, > sizeof(u64))) > return 1; > Queued, thanks. Paolo
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