linux-kernel - Re: [RFC 03/16] KVM: selftests: handle encryption bits in page tables

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Message-ID: <9de44944-57c1-047c-8c66-94eee6369a67@redhat.com>
Date:   Mon, 25 Oct 2021 09:34:10 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Michael Roth <michael.roth@....com>
Cc:     linux-kselftest@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Nathan Tempelman <natet@...gle.com>,
        Marc Orr <marcorr@...gle.com>,
        Steve Rutherford <srutherford@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Varad Gautam <varad.gautam@...e.com>,
        Shuah Khan <shuah@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Ricardo Koller <ricarkol@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC 03/16] KVM: selftests: handle encryption bits in page tables

On 24/10/21 18:49, Michael Roth wrote:
> So test code would need to consider cases where addr_gpa2raw() needs to be
> used to set the C-bit (which is basically only when they want to mix usage
> of the vm_phy_page[s]_alloc with their own mapping of the guest page tables,
> which doesn't seem to be done in any existing tests anyway).

Yes, and it seems like a more rare case in general.

> The library code would need these addr_gpa2raw() hooks in places where
> it calls virt_*map() internally. Probably just a handful of places
> though.

Either that, or you can have virt_*map that consults the encryption 
bitmap, and virt_*map_enc (or _raw, doesn't matter) that takes the 
encryption state explicitly as a bool.

> Even in this alternative approach though, having addr_gpa2hva() silently
> mask away C-bit still seems useful for the reasons above, but again, no
> strong feelings one way or the other on that.

Ok, keep it the way you find more useful.

Paolo