linux-kernel - Re: [PATCH v2 12/49] KVM: x86: Reject disabling of MWAIT/HLT interception when not allowed

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Message-ID: <ZpEwT59eveCC79uN@google.com>
Date: Fri, 12 Jul 2024 06:31:59 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Hou Wenlong <houwenlong.hwl@...group.com>, 
	Kechen Lu <kechenl@...dia.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Maxim Levitsky <mlevitsk@...hat.com>, Binbin Wu <binbin.wu@...ux.intel.com>, 
	Yang Weijiang <weijiang.yang@...el.com>, Robert Hoo <robert.hoo.linux@...il.com>
Subject: Re: [PATCH v2 12/49] KVM: x86: Reject disabling of MWAIT/HLT
 interception when not allowed

On Fri, Jul 12, 2024, Xiaoyao Li wrote:
> On 5/18/2024 1:38 AM, Sean Christopherson wrote:
> > @@ -6565,33 +6571,29 @@ 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())
> 
> sigh.
> 
> KVM_X86_DISABLE_VALID_EXITS has no user now. But we cannot remove it since
> it's in uapi header, right?

We can, actually.  Forcing userspace to make changes when userspace updates their
copy of the headers is ok (building directly against kernel headers is discouraged).