linux-kernel - Re: [PATCH 10/23] KVM: MMU: split cpu_role from mmu

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Message-ID: <04e568ee-8e44-dabe-2cc3-94b9c95287e1@redhat.com>
Date:   Sat, 5 Feb 2022 15:49:12 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        seanjc@...gle.com, vkuznets@...hat.com
Subject: Re: [PATCH 10/23] KVM: MMU: split cpu_role from mmu_role

On 2/4/22 22:57, David Matlack wrote:
>> +	vcpu->arch.root_mmu.cpu_role.base.level = 0;
>> +	vcpu->arch.guest_mmu.cpu_role.base.level = 0;
>> +	vcpu->arch.nested_mmu.cpu_role.base.level = 0;
> Will cpu_role.base.level already be 0 if CR0.PG=0 && !tdp_enabled? i.e.
> setting cpu_role.base.level to 0 might not have the desired effect.
> 
> It might not matter in practice since the shadow_mmu_init_context() and
> kvm_calc_mmu_role_common() check both the mmu_role and cpu_role, but does
> make this reset code confusing.
> 

Good point.  The (still unrealized) purpose of this series is to be able 
to check mmu_role only, so for now I'll just keep the valid bit in the 
ext part of the cpu_role.  The mmu_role's level however is never zero, 
so I can already use the level when I remove the ext part from the mmu_role.

I'll remove the valid bit of the ext part only after the cpu_role check 
is removed, because then it can trivially go.

Paolo