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Date: Tue, 16 Aug 2016 10:43:40 +0800 From: Wanpeng Li <kernellwp@...il.com> To: Radim Krčmář <rkrcmar@...hat.com> Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>, Jim Mattson <jmattson@...gle.com>, Wincy Van <fanwenyi0529@...il.com>, Paolo Bonzini <pbonzini@...hat.com>, Bandan Das <bsd@...hat.com> Subject: Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on MSR_IA32_APICBASE write 2016-08-09 2:16 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>: > If vmcs12 does not intercept APIC_BASE writes, then KVM will handle the > write with vmcs02 as the current VMCS. > This will incorrectly apply modifications intended for vmcs01 to vmcs02 > and L2 can use it to gain access to L0's x2APIC registers by disabling > virtualized x2APIC while using msr bitmap that assumes enabled. > > Postpone execution of vmx_set_virtual_x2apic_mode until vmcs01 is the > current VMCS. An alternative solution would temporarily make vmcs01 the > current VMCS, but it requires more care. > > Fixes: 8d14695f9542 ("x86, apicv: add virtual x2apic support") > Reported-by: Jim Mattson <jmattson@...gle.com> > Signed-off-by: Radim Krčmář <rkrcmar@...hat.com> Reviewed-by: Wanpeng Li <wanpeng.li@...mail.com> > --- > arch/x86/kvm/vmx.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index c66ac2c70d22..ae111a07acc4 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -422,6 +422,7 @@ struct nested_vmx { > struct list_head vmcs02_pool; > int vmcs02_num; > u64 vmcs01_tsc_offset; > + bool change_vmcs01_virtual_x2apic_mode; > /* L2 must run next, and mustn't decide to exit to L1. */ > bool nested_run_pending; > /* > @@ -8424,6 +8425,12 @@ static void vmx_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set) > { > u32 sec_exec_control; > > + /* Postpone execution until vmcs01 is the current VMCS. */ > + if (is_guest_mode(vcpu)) { > + to_vmx(vcpu)->nested.change_vmcs01_virtual_x2apic_mode = true; > + return; > + } > + > /* > * There is not point to enable virtualize x2apic without enable > * apicv > @@ -10749,6 +10756,12 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason, > vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL, > PIN_BASED_VMX_PREEMPTION_TIMER); > > + if (vmx->nested.change_vmcs01_virtual_x2apic_mode) { > + vmx->nested.change_vmcs01_virtual_x2apic_mode = false; > + vmx_set_virtual_x2apic_mode(vcpu, > + vcpu->arch.apic_base & X2APIC_ENABLE); > + } > + > /* This is needed for same reason as it was needed in prepare_vmcs02 */ > vmx->host_rsp = 0;
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