linux-kernel - Re: [RFC 14/33] KVM: x86: Add VTL to the MMU role

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Message-ID: <ZUvE2clQI-wOzRBd@google.com>
Date:   Wed, 8 Nov 2023 09:26:49 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Nicolas Saenz Julienne <nsaenz@...zon.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, anelkz@...zon.com, graf@...zon.com,
        dwmw@...zon.co.uk, jgowans@...zon.com, corbert@....net,
        kys@...rosoft.com, haiyangz@...rosoft.com, decui@...rosoft.com,
        x86@...nel.org, linux-doc@...r.kernel.org
Subject: Re: [RFC 14/33] KVM: x86: Add VTL to the MMU role

On Wed, Nov 08, 2023, Nicolas Saenz Julienne wrote:
> With the upcoming introduction of per-VTL memory protections, make MMU
> roles VTL aware. This will avoid sharing PTEs between vCPUs that belong
> to different VTLs, and that have distinct memory access restrictions.
> 
> Four bits are allocated to store the VTL number in the MMU role, since
> the TLFS states there is a maximum of 16 levels.

How many does KVM actually allow/support?  Multiplying the number of possible
roots by 16x is a *major* change.