Re: [PATCH v4 17/17] kvm: vmx: Emulate TEST_CTL MSR

[Xiaoyao Li]

On Mon, 2019-03-11 at 16:21 +0100, Paolo Bonzini wrote:
> On 11/03/19 16:10, Xiaoyao Li wrote:
> > On Mon, 2019-03-11 at 14:31 +0100, Paolo Bonzini wrote:
> > > On 09/03/19 03:31, Xiaoyao Li wrote:
> > > > Hi, Paolo,
> > > > 
> > > > Do you have any comments on this patch?
> > > > 
> > > > We are preparing v5 patches for split lock detection, if you have any
> > > > comments
> > > > about this one, please let me know.
> > > 
> > > No, my only comment is that it should be placed _before_ the other two
> > > for bisectability.  I think I have already sent that small remark.
> > > 
> > > Thanks,
> > > 
> > > Paolo
> > 
> > I cannot find the small remark you sent before. Maybe I missed something.
> > But I'am confused why it should be placed _before_ the other two. This patch
> > just use the vmx->core_capability that defined it the previous patch.
> 
> Because otherwise the guest can see core_capability != 0 and will #GP
> when trying to use split lock detection.
> 
> But you are right, this patch must be the last.  Instead,
> kvm-get_core_capability() should always return  0 until the previous
> patch.  Then in this patch you add the rdmsr and boot_cpu_has() tests.
> 
> Paolo

Hi, Paolo

Thanks a lot for your explanation. It makes me better understand the
bisectability of a patchset. I really appreciate you and I love the community. I
can learn a lot here and it makes me better.

I will fix the bisectability issue following your comments.

> > > > > +		if (!(vmx->core_capability &
> > > > > CORE_CAP_SPLIT_LOCK_DETECT))
> > > > > +			return 1;
> > > > > +
> > > > > +		if (data & ~TEST_CTL_ENABLE_SPLIT_LOCK_DETECT)
> > > > > +			return 1;
> > > > > +		vmx->msr_test_ctl = data;
> > > > > +		break;
> > > > >  	case MSR_EFER:
> > > > >  		ret = kvm_set_msr_common(vcpu, msr_info);
> > > > >  		break;
> > > > > @@ -4108,6 +4122,9 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
> > > > >  
> > > > >  	vmx->arch_capabilities = kvm_get_arch_capabilities();
> > > > >  
> > > > > +	/* disable AC split lock by default */
> > > > > +	vmx->msr_test_ctl = 0;
> > > > > +
> > > > >  	vm_exit_controls_init(vmx, vmx_vmexit_ctrl());
> > > > >  
> > > > >  	/* 22.2.1, 20.8.1 */
> > > > > @@ -4145,6 +4162,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu
> > > > > *vcpu,
> > > > > bool
> > > > > init_event)
> > > > >  
> > > > >  	vmx->rmode.vm86_active = 0;
> > > > >  	vmx->spec_ctrl = 0;
> > > > > +	vmx->msr_test_ctl = 0;
> > > > >  
> > > > >  	vcpu->arch.microcode_version = 0x100000000ULL;
> > > > >  	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
> > > > > @@ -6344,6 +6362,21 @@ static void atomic_switch_perf_msrs(struct
> > > > > vcpu_vmx
> > > > > *vmx)
> > > > >  					msrs[i].host, false);
> > > > >  }
> > > > >  
> > > > > +static void atomic_switch_msr_test_ctl(struct vcpu_vmx *vmx)
> > > > > +{
> > > > > +	u64 host_msr_test_ctl;
> > > > > +
> > > > > +	if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
> > > > > +		return;
> > > > > +
> > > > > +	rdmsrl(MSR_TEST_CTL, host_msr_test_ctl);
> > > > > +	if (host_msr_test_ctl == vmx->msr_test_ctl)
> > > > > +		clear_atomic_switch_msr(vmx, MSR_TEST_CTL);
> > > > > +	else
> > > > > +		add_atomic_switch_msr(vmx, MSR_TEST_CTL, vmx-
> > > > > >msr_test_ctl,
> > > > > +				      host_msr_test_ctl, false);
> > > > > +}
> > > > > +
> > > > >  static void vmx_arm_hv_timer(struct vcpu_vmx *vmx, u32 val)
> > > > >  {
> > > > >  	vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, val);
> > > > > @@ -6585,6 +6618,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> > > > >  
> > > > >  	atomic_switch_perf_msrs(vmx);
> > > > >  
> > > > > +	atomic_switch_msr_test_ctl(vmx);
> > > > > +
> > > > >  	vmx_update_hv_timer(vcpu);
> > > > >  
> > > > >  	/*
> > > > > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> > > > > index cc22379991f3..e8831609c6c3 100644
> > > > > --- a/arch/x86/kvm/vmx/vmx.h
> > > > > +++ b/arch/x86/kvm/vmx/vmx.h
> > > > > @@ -191,6 +191,7 @@ struct vcpu_vmx {
> > > > >  	u64		      msr_guest_kernel_gs_base;
> > > > >  #endif
> > > > >  
> > > > > +	u64		      msr_test_ctl;
> > > > >  	u64		      core_capability;
> > > > >  	u64		      arch_capabilities;
> > > > >  	u64		      spec_ctrl;
> > > 
> > > 
> 
>