linux-kernel - Re: [PATCH v4 19/32] KVM: x86: Explicitly track all possibilities for APIC map's logical modes

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Date:   Fri, 16 Dec 2022 23:34:29 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Alejandro Jimenez <alejandro.j.jimenez@...cle.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Li RongQing <lirongqing@...du.com>
Subject: Re: [PATCH v4 19/32] KVM: x86: Explicitly track all possibilities
 for APIC map's logical modes

On Fri, Dec 16, 2022, Sean Christopherson wrote:
> On Thu, Dec 08, 2022, Maxim Levitsky wrote:

...

> > > @@ -282,7 +291,8 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
> > >  		if (!apic_x2apic_mode(apic) && !new->phys_map[xapic_id])
> > >  			new->phys_map[xapic_id] = apic;
> > >  
> > > -		if (!kvm_apic_sw_enabled(apic))
> > > +		if (new->logical_mode == KVM_APIC_MODE_MAP_DISABLED ||
> > > +		    !kvm_apic_sw_enabled(apic))
> > >  			continue;
> > Very minor nitpick: it feels to me that code that updates the logical mode of the
> > map, might be better to be in a function, or in 'if', like
> 
> An if-statement would be rough due to the indentation.  A function works well
> though, especially if both the physical and logical chunks are put into helpers.
> E.g. the patch at the bottom (with other fixup for this patch) yields:
> 
> 	new->max_apic_id = max_id;
> 	new->logical_mode = KVM_APIC_MODE_SW_DISABLED;
> 
> 	kvm_for_each_vcpu(i, vcpu, kvm) {
> 		if (!kvm_apic_present(vcpu))
> 			continue;
> 
> 		if (kvm_recalculate_phys_map(new, vcpu, &xapic_id_mismatch)) {
> 			kvfree(new);
> 			new = NULL;
> 			goto out;
> 		}
> 
> 		kvm_recalculate_logical_map(new, vcpu);
> 	}
> 
> I'll tack that patch on at the end of the series if it looks ok.

...

> +static void kvm_recalculate_logical_map(struct kvm_apic_map *new,
> +					struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_lapic *apic = vcpu->arch.apic;
> +	enum kvm_apic_logical_mode logical_mode;
> +	struct kvm_lapic **cluster;
> +	u16 mask;
> +	u32 ldr;
> +
> +	if (new->logical_mode == KVM_APIC_MODE_MAP_DISABLED)
> +		return;
> +
> +	if (kvm_apic_sw_enabled(apic))

"minor" detail, this is inverted.