Re: [RFC PATCH v6 3/6] KVM: x86: Reject disabling of MWAIT interception when not allowed

[Zhao Liu]

On Sat, Jan 21, 2023 at 02:07:35AM +0000, Kechen Lu wrote:
> Date: Sat, 21 Jan 2023 02:07:35 +0000
> From: Kechen Lu <kechenl@xxxxxxxxxx>
> Subject: [RFC PATCH v6 3/6] KVM: x86: Reject disabling of MWAIT
>  interception when not allowed
> X-Mailer: git-send-email 2.34.1
> 
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> 
> Reject KVM_CAP_X86_DISABLE_EXITS if userspace attempts to disable MWAIT
> exits and KVM previously reported (via KVM_CHECK_EXTENSION) that MWAIT is
> not allowed in guest, e.g. because it's not supported or the CPU doesn't
> have an aways-running

nit: always-running?

> APIC timer.
> 
> Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Kechen Lu <kechenl@xxxxxxxxxx>
> ---
>  arch/x86/kvm/x86.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a77b55142c6..60caa3fd40e5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4326,6 +4326,16 @@ static inline bool kvm_can_mwait_in_guest(void)
>  		boot_cpu_has(X86_FEATURE_ARAT);
>  }
>  
> +static u64 kvm_get_allowed_disable_exits(void)
> +{
> +	u64 r = KVM_X86_DISABLE_VALID_EXITS;
> +
> +	if (!kvm_can_mwait_in_guest())
> +		r &= ~KVM_X86_DISABLE_EXITS_MWAIT;
> +
> +	return r;
> +}
> +
>  static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
>  					    struct kvm_cpuid2 __user *cpuid_arg)
>  {
> @@ -4448,10 +4458,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		r = KVM_CLOCK_VALID_FLAGS;
>  		break;
>  	case KVM_CAP_X86_DISABLE_EXITS:
> -		r |=  KVM_X86_DISABLE_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
> -		      KVM_X86_DISABLE_EXITS_CSTATE;
> -		if(kvm_can_mwait_in_guest())
> -			r |= KVM_X86_DISABLE_EXITS_MWAIT;
> +		r |= kvm_get_allowed_disable_exits();
>  		break;
>  	case KVM_CAP_X86_SMM:
>  		if (!IS_ENABLED(CONFIG_KVM_SMM))
> @@ -6224,15 +6231,14 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  		break;
>  	case KVM_CAP_X86_DISABLE_EXITS:
>  		r = -EINVAL;
> -		if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)
> +		if (cap->args[0] & ~kvm_get_allowed_disable_exits())
>  			break;
>  
>  		mutex_lock(&kvm->lock);
>  		if (kvm->created_vcpus)
>  			goto disable_exits_unlock;
>  
> -		if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
> -			kvm_can_mwait_in_guest())
> +		if (cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT)
>  			kvm->arch.mwait_in_guest = true;
>  		if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
>  			kvm->arch.hlt_in_guest = true;
> -- 
> 2.34.1
>