linux-kernel - Re: [RFC PATCH v3 3/7] KVM: x86: Reject disabling of MWAIT interception when not allowed

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Date:   Wed, 20 Jul 2022 17:13:42 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Kechen Lu <kechenl@...dia.com>
Cc:     kvm@...r.kernel.org, pbonzini@...hat.com, vkuznets@...hat.com,
        somduttar@...dia.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 3/7] KVM: x86: Reject disabling of MWAIT
 interception when not allowed

On Tue, Jun 14, 2022, Kechen Lu wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> 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 APIC timer.
> 
> Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/x86.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b419b258ed90..f31ebbb1b94f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4199,6 +4199,17 @@ 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_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
> +		KVM_X86_DISABLE_EXITS_CSTATE;
> +
> +	if(kvm_can_mwait_in_guest())

Probably my fault for not fixing this during copy+paste, but add a space after the if, i.e.

	if (kvm_can_mwait_in_guest())

> +		r |= KVM_X86_DISABLE_EXITS_MWAIT;
> +
> +	return r;
> +}