Messages in this thread | | | From | Wincy Van <> | Date | Wed, 4 Mar 2015 13:27:37 +0800 | Subject | Re: [PATCH] KVM: vmx: Set msr bitmap correctly if vcpu is in guest mode |
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On Wed, Mar 4, 2015 at 12:04 PM, Bandan Das <bsd@redhat.com> wrote: > Wincy Van <fanwenyi0529@gmail.com> writes: > >> On Wed, Mar 4, 2015 at 1:39 AM, Bandan Das <bsd@redhat.com> wrote: >>> Wincy Van <fanwenyi0529@gmail.com> writes: >>> >>>> In commit 3af18d9c5fe9 ("KVM: nVMX: Prepare for using hardware MSR bitmap"), >>>> we are setting MSR_BITMAP in prepare_vmcs02 if we should use hardware. This >>>> is not enough since the field will be modified by following vmx_set_efer. >>>> >>>> Fix this by setting vmx_msr_bitmap_nested in vmx_set_msr_bitmap if vcpu is >>>> in guest mode. >>>> >>>> Signed-off-by: Wincy Van <fanwenyi0529@gmail.com> >>>> --- >>>> arch/x86/kvm/vmx.c | 5 ++++- >>>> 1 files changed, 4 insertions(+), 1 deletions(-) >>>> >>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>> index f7b20b4..f6e3457 100644 >>>> --- a/arch/x86/kvm/vmx.c >>>> +++ b/arch/x86/kvm/vmx.c >>>> @@ -2168,7 +2168,10 @@ static void vmx_set_msr_bitmap(struct kvm_vcpu *vcpu) >>>> { >>>> unsigned long *msr_bitmap; >>>> >>>> - if (irqchip_in_kernel(vcpu->kvm) && apic_x2apic_mode(vcpu->arch.apic)) { >>>> + if (is_guest_mode(vcpu)) >>>> + msr_bitmap = vmx_msr_bitmap_nested; >>>> + else if (irqchip_in_kernel(vcpu->kvm) && >>>> + apic_x2apic_mode(vcpu->arch.apic)) { >>> >>> So, we end up writing the MSR_BITMAP field twice - once when we >>> call nested_vmx_merge_msr_bitmap() and another here. Why don't we just >>> remove the former since prepare_vmcs02 will call vmx_set_efer anyway ? >>> >> >> Yes, setting MSR_BITMAP twice is redundant, but we can not rely on >> vmx_set_efer to set that field, this is not vmx_set_efer 's duty. > It's not. The change is in vmx_set_msr_bitmap() and vmx_set_efer > happens to call it. The call to the merge function may very well > belong to prepare_vmcs02() but the write to the vmcs field could > belong to vmx_set_msr_bitmap. > >> Consider that someone wants to make some changes on loading >> L2's efer, he may be confused about this. We should reduce the >> degree of code coupling. > Fine, just add a comment in prepare_vmcs02 that that's where the field > is being set. No point in doing the same thing twice. >
Yes, Agreed. I'll send v2 ASAP.
Thanks, Wincy
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