Re: [PATCH v2] KVM: x86: Don't leave APF half-enabled on bad APF data GPA

[Sean Christopherson <seanjc@google.com>]

Thanks for posting this!  My "week" estimate was wee bit off...

On Fri, Apr 03, 2026, Ethan Yang wrote:
>  static inline u64 pdptr_rsvd_bits(struct kvm_vcpu *vcpu)
> @@ -3616,6 +3621,7 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
>  {
>  	gpa_t gpa = data & ~0x3f;
> +	bool enable;
>  
>  	/* Bits 4:5 are reserved, Should be zero */
>  	if (data & 0x30)
> @@ -3632,18 +3638,20 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
>  	if (!lapic_in_kernel(vcpu))
>  		return data ? 1 : 0;
>  
> +	enable = __kvm_pv_async_pf_enabled(data);
> +
> +	if (enable &&
> +	    kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
> +				      sizeof(u64)))

I would rather forgo a local variable and either hhave the below check stay as
kvm_pv_async_pf_enabled() or just redo the call to __kvm_pv_async_pf_enabled().

> +		return 1;

Newline please.

>  	vcpu->arch.apf.msr_en_val = data;
>  
> -	if (!kvm_pv_async_pf_enabled(vcpu)) {
> +	if (!enable) {
>  		kvm_clear_async_pf_completion_queue(vcpu);
>  		kvm_async_pf_hash_reset(vcpu);
>  		return 0;
>  	}
>  
> -	if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
> -					sizeof(u64)))
> -		return 1;
> -
>  	vcpu->arch.apf.send_always = (data & KVM_ASYNC_PF_SEND_ALWAYS);
>  	vcpu->arch.apf.delivery_as_pf_vmexit = data & KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT;

As I sketched out, in a follow-up patch, I would like to to update these fields
as well.  I don't like tracking stale information, even if it _should_ be unused.

Actually, even better, just drop the fields.  That way zeroing msr_en_val via
INIT won't lead to stale data either.

I'll post a v3, should be easier overall than posting diffs for the suggestions
and then making you write changelogs :-)