linux-kernel - Re: [PATCH v3 08/12] KVM: arm/arm64: Check vcpu redist base before registering an iodev

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Message-ID: <20180426101256.GC19872@C02W217FHV2R.local>
Date:   Thu, 26 Apr 2018 12:12:56 +0200
From:   Christoffer Dall <christoffer.dall@....com>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        marc.zyngier@....com, cdall@...nel.org, peter.maydell@...aro.org,
        andre.przywara@....com, drjones@...hat.com, wei@...hat.com
Subject: Re: [PATCH v3 08/12] KVM: arm/arm64: Check vcpu redist base before
 registering an iodev

On Thu, Apr 26, 2018 at 11:25:06AM +0200, Auger Eric wrote:
> Hi Christoffer,
> 
> On 04/24/2018 11:07 PM, Christoffer Dall wrote:
> > On Fri, Apr 13, 2018 at 10:20:54AM +0200, Eric Auger wrote:
> >> As we are going to register several redist regions,
> >> vgic_register_all_redist_iodevs() may be called several times. We need
> >> to register a redist_iodev for a given vcpu only once. 
> > 
> > Wouldn't it be more natural to change that caller to only register the
> > iodevs for that region?
> 
> vgic_register_redist_iodev() is the place where we decide where we map a
> given vcpu redist into a given redist region.
> 
> Calling vgic_register_redist_iodev for only the vcpus mapping to the
> redist region would force to inverse the logic. I think it would bring
> more upheavals in the code than bringing benefit?
> 
> This new check somehow corresponds to what we had before:
> "
> if (IS_VGIC_ADDR_UNDEF(vgic->vgic_redist_base))
>                 return 0;
> "

Ah, this is because we don't enforce any ordering between creating the
redistributors and initializing the vcpus, this always confuses me.

Fine, let's leave it as you suggest here.

Thanks,
-Christoffer