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From: Nikita Leshenko <nikita.leshchenko@oracle.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: kvm@vger.kernel.org, Liran Alon <liran.alon@oracle.com>,
	Joao Martins <joao.m.martins@oracle.com>
Subject: Re: [PATCH] KVM: nVMX: Check that HLT activity state is supported
Date: Wed, 14 Aug 2019 09:59:57 +0300	[thread overview]
Message-ID: <AD04DDAB-9655-4B41-A9D8-95DA62767C11@oracle.com> (raw)
In-Reply-To: <20190813143501.GA13991@linux.intel.com>



> On 13 Aug 2019, at 17:35, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> 
> On Tue, Aug 13, 2019 at 04:13:03PM +0300, Nikita Leshenko wrote:
>> Fail VM entry if GUEST_ACTIVITY_HLT is unsupported. According to "SDM A.6 -
>> Miscellaneous Data", VM entry should fail if the HLT activity is not marked as
>> supported on IA32_VMX_MISC MSR.
>> 
>> Usermode might disable GUEST_ACTIVITY_HLT support in the vCPU with
>> vmx_restore_vmx_misc(). Before this commit VM entries would have succeeded
>> anyway.
> 
> Is there a use case for disabling GUEST_ACTIVITY_HLT?  Or can we simply
> disallow writes to IA32_VMX_MISC that disable GUEST_ACTIVITY_HLT?

I don't have a specific case for disabling it. Disallowing turning it off in IA32_VMX_MISC
is also possible. Because of what you said below I will submit a different patch that does
so.

Nikita

> 
> To disable GUEST_ACTIVITY_HLT, userspace also has to make
> CPU_BASED_HLT_EXITING a "must be 1" control, otherwise KVM will be
> presenting a bogus model to L1.
> 
> The bad model is visible to L1 if CPU_BASED_HLT_EXITING is set by L0,
> i.e. KVM is running without kvm_hlt_in_guest(), and cleared by L1.  In
> that case, a HLT from L2 will be handled in L0.  L0 will set the state to
> KVM_MP_STATE_HALTED and report to L1 (on a nested VM-Exit, e.g. INTR),
> that the activity state is GUEST_ACTIVITY_HLT, which from L1's perspective
> doesn't exist.
> 
>> Reviewed-by: Liran Alon <liran.alon@oracle.com>
>> Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
>> Signed-off-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
>> ---
>> arch/x86/kvm/vmx/nested.c | 16 ++++++++++++----
>> arch/x86/kvm/vmx/nested.h |  5 +++++
>> 2 files changed, 17 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index 46af3a5e9209..3165e2f7992f 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -2656,11 +2656,19 @@ static int nested_vmx_check_vmcs_link_ptr(struct kvm_vcpu *vcpu,
>> /*
>>  * Checks related to Guest Non-register State
>>  */
>> -static int nested_check_guest_non_reg_state(struct vmcs12 *vmcs12)
>> +static int nested_check_guest_non_reg_state(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>> {
>> -	if (vmcs12->guest_activity_state != GUEST_ACTIVITY_ACTIVE &&
>> -	    vmcs12->guest_activity_state != GUEST_ACTIVITY_HLT)
>> +	switch (vmcs12->guest_activity_state) {
>> +	case GUEST_ACTIVITY_ACTIVE:
>> +		/* Always supported */
>> +		break;
>> +	case GUEST_ACTIVITY_HLT:
>> +		if (!nested_cpu_has_activity_state_hlt(vcpu))
>> +			return -EINVAL;
>> +		break;
>> +	default:
>> 		return -EINVAL;
>> +	}
>> 
>> 	return 0;
>> }
>> @@ -2710,7 +2718,7 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
>> 	     (vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD)))
>> 		return -EINVAL;
>> 
>> -	if (nested_check_guest_non_reg_state(vmcs12))
>> +	if (nested_check_guest_non_reg_state(vcpu, vmcs12))
>> 		return -EINVAL;
>> 
>> 	return 0;
>> diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
>> index e847ff1019a2..4a294d3ff820 100644
>> --- a/arch/x86/kvm/vmx/nested.h
>> +++ b/arch/x86/kvm/vmx/nested.h
>> @@ -123,6 +123,11 @@ static inline bool nested_cpu_has_zero_length_injection(struct kvm_vcpu *vcpu)
>> 	return to_vmx(vcpu)->nested.msrs.misc_low & VMX_MISC_ZERO_LEN_INS;
>> }
>> 
>> +static inline bool nested_cpu_has_activity_state_hlt(struct kvm_vcpu *vcpu)
>> +{
>> +	return to_vmx(vcpu)->nested.msrs.misc_low & VMX_MISC_ACTIVITY_HLT;
>> +}
>> +
>> static inline bool nested_cpu_supports_monitor_trap_flag(struct kvm_vcpu *vcpu)
>> {
>> 	return to_vmx(vcpu)->nested.msrs.procbased_ctls_high &
>> -- 
>> 2.20.1
>> 


      reply	other threads:[~2019-08-14  7:00 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 13:13 [PATCH] KVM: nVMX: Check that HLT activity state is supported Nikita Leshenko
2019-08-13 14:35 ` Sean Christopherson
2019-08-14  6:59   ` Nikita Leshenko [this message]

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