Re: [PATCH] KVM: x86: Add emulation of MSR_SMI_COUNT

[Paolo Bonzini <pbonzini@redhat.com>]

On 04/12/2017 10:27, David Hildenbrand wrote:
> On 15.11.2017 12:43, Liran Alon wrote:
>> This MSR returns the number of #SMIs that occurred on CPU since
>> boot.
>>
>> It was seen to be used frequently by ESXi guest.
>>
>> Patch adds a new vcpu-arch specific var called smi_count to
>> save the number of #SMIs which occurred on CPU since boot.
>> It is exposed as a read-only MSR to guest (causing #GP
>> on wrmsr) in RDMSR/WRMSR emulation code.
>> MSR_SMI_COUNT is also added to emulated_msrs[] to make sure
>> user-space can save/restore it for migration purposes.
>>
>> Signed-off-by: Liran Alon <liran.alon@oracle.com>
>> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
>> Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
>> Reviewed-by: Bhavesh Davda <bhavesh.davda@oracle.com>
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> ---
>>
>> Notes:
>>     To make vmsave/vload work for MSR_SMI_COUNT (for migration purposes),
>>     a patch for QEMU is also required.
>>     We have written such patch and verified that it works.
>>     It will be submitted seperately to the QEMU mailing list.
>>
>>  arch/x86/include/asm/kvm_host.h |  1 +
>>  arch/x86/kvm/x86.c              | 11 +++++++++++
>>  2 files changed, 12 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index c73e493adf07..089856eeac5d 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -504,6 +504,7 @@ struct kvm_vcpu_arch {
>>  	int mp_state;
>>  	u64 ia32_misc_enable_msr;
>>  	u64 smbase;
>> +	u64 smi_count;
>>  	bool tpr_access_reporting;
>>  	u64 ia32_xss;
>>  
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 21c00594f230..dedf5539f924 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1036,6 +1036,7 @@ bool kvm_rdpmc(struct kvm_vcpu *vcpu)
>>  	MSR_IA32_MCG_CTL,
>>  	MSR_IA32_MCG_EXT_CTL,
>>  	MSR_IA32_SMBASE,
>> +	MSR_SMI_COUNT,
>>  	MSR_PLATFORM_INFO,
>>  	MSR_MISC_FEATURES_ENABLES,
>>  };
>> @@ -2217,6 +2218,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>  			return 1;
>>  		vcpu->arch.smbase = data;
>>  		break;
>> +	case MSR_SMI_COUNT:
>> +		if (!msr_info->host_initiated)
>> +			return 1;
>> +		vcpu->arch.smi_count = data;
>> +		break;
>>  	case MSR_KVM_WALL_CLOCK_NEW:
>>  	case MSR_KVM_WALL_CLOCK:
>>  		vcpu->kvm->arch.wall_clock = data;
>> @@ -2491,6 +2497,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>  			return 1;
>>  		msr_info->data = vcpu->arch.smbase;
>>  		break;
>> +	case MSR_SMI_COUNT:
>> +		msr_info->data = vcpu->arch.smi_count;
>> +		break;
>>  	case MSR_IA32_PERF_STATUS:
>>  		/* TSC increment by tick */
>>  		msr_info->data = 1000ULL;
>> @@ -6437,6 +6446,7 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
>>  		kvm_x86_ops->queue_exception(vcpu);
>>  	} else if (vcpu->arch.smi_pending && !is_smm(vcpu)) {
>>  		vcpu->arch.smi_pending = false;
>> +		++vcpu->arch.smi_count;
>>  		enter_smm(vcpu);
>>  	} else if (vcpu->arch.nmi_pending && kvm_x86_ops->nmi_allowed(vcpu)) {
>>  		--vcpu->arch.nmi_pending;
>> @@ -7781,6 +7791,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>  	vcpu->arch.hflags = 0;
>>  
>>  	vcpu->arch.smi_pending = 0;
>> +	vcpu->arch.smi_count = 0;
>>  	atomic_set(&vcpu->arch.nmi_queued, 0);
>>  	vcpu->arch.nmi_pending = 0;
>>  	vcpu->arch.nmi_injected = false;
>>
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> 
> (only wondering if we have to make availability depend on e.g. a
> KVM_CAP, so a guest will not silently start using it, although migration
> with old QEMUs is broken)

No need for a capability, old QEMU will just reset to 0 on migration.

Paolo