linux-kernel - Re: [PATCH 15/19] KVM: x86: Explicitly skip optimized logical map setup if vCPU's LDR==0

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Date:   Wed, 31 Aug 2022 16:47:25 +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,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Li RongQing <lirongqing@...du.com>
Subject: Re: [PATCH 15/19] KVM: x86: Explicitly skip optimized logical map
 setup if vCPU's LDR==0

On Wed, Aug 31, 2022, Maxim Levitsky wrote:
> On Wed, 2022-08-31 at 00:35 +0000, Sean Christopherson wrote:
> > Explicitly skip the optimized map setup if the vCPU's LDR is '0', i.e. if
> > the vCPU will never response to logical mode interrupts.  KVM already
> > skips setup in this case, but relies on kvm_apic_map_get_logical_dest()
> > to generate mask==0.  KVM still needs the mask=0 check as a non-zero LDR
> > can yield mask==0 depending on the mode, but explicitly handling the LDR
> > will make it simpler to clean up the logical mode tracking in the future.
> 
> If I am not mistaken, the commit description is a bit misleading - in this
> case we just don't add the vCPU to the map since it is unreachable, but we do
> continue creating the map.

I'll reword.  I intended that to mean "skip the optimized setup for the vCPU", but
even that is unnecessarily confusing.