KVM: nested VMX: disable perf cpuid reporting

KVM: nested VMX: disable perf cpuid reporting

[Marcelo Tosatti]

Initilization of L2 guest with -cpu host, on L1 guest with -cpu host 
triggers:

(qemu) KVM: entry failed, hardware error 0x7
...
nested_vmx_run: VMCS MSR_{LOAD,STORE} unsupported

Nested VMX MSR load/store support is not sufficient to 
allow perf for L2 guest.

Until properly fixed, trap CPUID and disable function 0xA.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index e28d798..976e3a5 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -774,6 +774,12 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
 	if (!best)
 		best = check_cpuid_limit(vcpu, function, index);
 
+	/*
+	 * Perfmon not yet supported for L2 guest.
+	 */
+	if (is_guest_mode(vcpu) && function == 0xa)
+		best = NULL;
+
 	if (best) {
 		*eax = best->eax;
 		*ebx = best->ebx;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e8f08e9..2ab5047 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6986,6 +6986,8 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
 	case EXIT_REASON_TASK_SWITCH:
 		return 1;
 	case EXIT_REASON_CPUID:
+		if (kvm_register_read(vcpu, VCPU_REGS_RAX) == 0xa)
+			return 0;
 		return 1;
 	case EXIT_REASON_HLT:
 		return nested_cpu_has(vmcs12, CPU_BASED_HLT_EXITING);

Re: KVM: nested VMX: disable perf cpuid reporting

[Paolo Bonzini]

Il 18/09/2014 23:24, Marcelo Tosatti ha scritto:
> 
> Initilization of L2 guest with -cpu host, on L1 guest with -cpu host 
> triggers:
> 
> (qemu) KVM: entry failed, hardware error 0x7
> ...
> nested_vmx_run: VMCS MSR_{LOAD,STORE} unsupported
> 
> Nested VMX MSR load/store support is not sufficient to 
> allow perf for L2 guest.
> 
> Until properly fixed, trap CPUID and disable function 0xA.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index e28d798..976e3a5 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -774,6 +774,12 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
>  	if (!best)
>  		best = check_cpuid_limit(vcpu, function, index);
>  
> +	/*
> +	 * Perfmon not yet supported for L2 guest.
> +	 */
> +	if (is_guest_mode(vcpu) && function == 0xa)
> +		best = NULL;
> +
>  	if (best) {
>  		*eax = best->eax;
>  		*ebx = best->ebx;
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index e8f08e9..2ab5047 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6986,6 +6986,8 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
>  	case EXIT_REASON_TASK_SWITCH:
>  		return 1;
>  	case EXIT_REASON_CPUID:
> +		if (kvm_register_read(vcpu, VCPU_REGS_RAX) == 0xa)
> +			return 0;
>  		return 1;
>  	case EXIT_REASON_HLT:
>  		return nested_cpu_has(vmcs12, CPU_BASED_HLT_EXITING);
> 

Nice solution. :)

Paolo

Re: KVM: nested VMX: disable perf cpuid reporting

[Marcelo Tosatti]

On Thu, Sep 18, 2014 at 06:24:57PM -0300, Marcelo Tosatti wrote:
> 
> Initilization of L2 guest with -cpu host, on L1 guest with -cpu host 
> triggers:
> 
> (qemu) KVM: entry failed, hardware error 0x7
> ...
> nested_vmx_run: VMCS MSR_{LOAD,STORE} unsupported
> 
> Nested VMX MSR load/store support is not sufficient to 
> allow perf for L2 guest.
> 
> Until properly fixed, trap CPUID and disable function 0xA.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Ping, Paolo?

Re: KVM: nested VMX: disable perf cpuid reporting

[Paolo Bonzini]

Il 22/09/2014 21:01, Marcelo Tosatti ha scritto:
> On Thu, Sep 18, 2014 at 06:24:57PM -0300, Marcelo Tosatti wrote:
>>
>> Initilization of L2 guest with -cpu host, on L1 guest with -cpu host 
>> triggers:
>>
>> (qemu) KVM: entry failed, hardware error 0x7
>> ...
>> nested_vmx_run: VMCS MSR_{LOAD,STORE} unsupported
>>
>> Nested VMX MSR load/store support is not sufficient to 
>> allow perf for L2 guest.
>>
>> Until properly fixed, trap CPUID and disable function 0xA.
>>
>> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> Ping, Paolo?
> 

Sorry, didn't push to kvm/queue but I've already applied the patch
locally.  I will do it first thing tomorrow (my workstation is off right
now so I cannot send you a SHA).

Paolo