Re: [PATCH v3 06/12] KVM: x86: don't disable APICv memslot when inhibited

[Paolo Bonzini]

Reviewing this patch and the next one together.

On 02/08/21 20:33, Maxim Levitsky wrote:
> +static int avic_alloc_access_page(struct kvm *kvm)
>  {
>  	void __user *ret;
>  	int r = 0;
>  
>  	mutex_lock(&kvm->slots_lock);
> +
> +	if (kvm->arch.apic_access_memslot_enabled)
>  		goto out;

This variable is overloaded between "is access enabled" and "is the 
memslot allocated".  I think you should check 
kvm->arch.apicv_inhibit_reasons instead in kvm_faultin_pfn.


> +	if (!activate)
> +		kvm_zap_gfn_range(kvm, gpa_to_gfn(APIC_DEFAULT_PHYS_BASE),
> +				  gpa_to_gfn(APIC_DEFAULT_PHYS_BASE + PAGE_SIZE));
> +

Off by one, the last argument of kvm_zap_gfn_range is inclusive:
Also, checking "activate" is a bit ugly when we have "new" available as 
well.  Yes, they are the same if !!old != !!new, but we care about the 
global state, not the single bit.

Putting everything together, this could become something like

        trace_kvm_apicv_update_request(activate, bit);
        if (!!old != !!new) {
		/*
		 * Kick all CPUs out of guest mode.  When
		 * kvm_vcpu_update_apicv succeeds in taking
		 * apicv_update_lock, it will see the
		 * new apicv_inhibit_reasons that we set below.
		 */
	        kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_UPDATE);

	        if (new) {
	                unsigned long gfn = gpa_to_gfn(APIC_DEFAULT_PHYS_BASE);
	                kvm_zap_gfn_range(kvm, gfn, gfn);
	        }
	}
        kvm->arch.apicv_inhibit_reasons = new;
        mutex_unlock(&kvm->arch.apicv_update_lock);

Paolo