Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <a7cc6ead-c30b-4d21-c92c-faf37d9023b7@redhat.com>
Date:   Sat, 5 Feb 2022 15:50:49 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [PATCH 03/23] KVM: MMU: remove valid from extended role
Content-Language: en-US
To:     David Matlack <dmatlack@google.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        seanjc@google.com, vkuznets@redhat.com
References: <20220204115718.14934-1-pbonzini@redhat.com>
 <20220204115718.14934-4-pbonzini@redhat.com> <Yf1xU+EVukcX4Exb@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <Yf1xU+EVukcX4Exb@google.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2/4/22 19:32, David Matlack wrote:
>> -	vcpu->arch.root_mmu.mmu_role.ext.valid = 0;
>> -	vcpu->arch.guest_mmu.mmu_role.ext.valid = 0;
>> -	vcpu->arch.nested_mmu.mmu_role.ext.valid = 0;
>> +	vcpu->arch.root_mmu.mmu_role.base.level = 0;
>> +	vcpu->arch.guest_mmu.mmu_role.base.level = 0;
>> +	vcpu->arch.nested_mmu.mmu_role.base.level = 0;
> I agree this will work but I think it makes the code more difficult to
> follow (and I start worrying that some code that relies on level being
> accurate will creep in in the future). At minimum we should extend the
> comment here to describe why level is being changed.
> 
> I did a half-assed attempt to pass something like "bool force_role_reset"
> down to the MMU initialization functions as an alternative but it very
> quickly got out of hand.
> 
> What about just changing `valid` to `cpuid_stale` and flip the meaning?
> kvm_mmu_after_set_cpuid() would set the cpuid_stale bit and then reset
> the MMUs.
> 

For now I'll swap this patch with one that clears the whole word, but 
keep the ext bit as described in my other reply.

Paolo