linux-kernel - Re: [PATCH v2 5/8] KVM: x86/mmu: Use separate namespaces for guest PTEs and shadow PTEs

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Message-ID: <7355b23b-d1ca-0050-4acf-e4a9a15adffa@redhat.com>
Date:   Wed, 15 Jun 2022 16:34:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>
Subject: Re: [PATCH v2 5/8] KVM: x86/mmu: Use separate namespaces for guest
 PTEs and shadow PTEs

On 6/15/22 16:26, Sean Christopherson wrote:
>> +		 * For example, a 4-byte PDE consumes bits 31:22 and an 8-byte PDE
>> +		 * consumes bits 29:21.  Each guest PD must be expanded into four
>> +		 * shadow PDs, one for each value of bits 31:30, and the PDPEs
>> +		 * will use the four quadrants in round-robin fashion.
> It's not round-robin, that would imply KVM rotates through each quadrant on its
> own.  FWIW, I like David's comment from his patch that simplifies this mess in a
> similar way.
> 
> https://lore.kernel.org/all/20220516232138.1783324-5-dmatlack@google.com

Yeah, by round-robin I meant that the 512 entries will look like q=0 q=1 
q=2 q=3 q=0 q=1 etc.

I'll incorporate David's comment, minus the last paragraph.

Paolo