linux-kernel - Re: [PATCH v8 5/8] KVM: Register/unregister the guest private memory regions

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Message-ID: <CA+EHjTzR6DwU950gud1opEGCNqCfiEvA4-JFtyJ0NBgTD-uHNg@mail.gmail.com>
Date:   Wed, 19 Oct 2022 19:32:21 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>, wei.w.wang@...el.com
Subject: Re: [PATCH v8 5/8] KVM: Register/unregister the guest private memory regions

On Wed, Oct 19, 2022 at 5:09 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Wed, Oct 19, 2022, Fuad Tabba wrote:
> > > > > This sounds good. Thank you.
> > > >
> > > > I like the idea of a separate Kconfig, e.g. CONFIG_KVM_GENERIC_PRIVATE_MEM or
> > > > something.  I highly doubt there will be any non-x86 users for multiple years,
> > > > if ever, but it would allow testing the private memory stuff on ARM (and any other
> > > > non-x86 arch) without needing full pKVM support and with only minor KVM
> > > > modifications, e.g. the x86 support[*] to test UPM without TDX is shaping up to be
> > > > trivial.
> > >
> > > CONFIG_KVM_GENERIC_PRIVATE_MEM looks good to me.
> >
> > That sounds good to me, and just keeping the xarray isn't really an
> > issue for pKVM.
>
> The xarray won't exist for pKVM if the #ifdefs in this patch are changed from
> CONFIG_HAVE_KVM_PRIVATE_MEM => CONFIG_KVM_GENERIC_PRIVATE_MEM.
>
> > We could end up using it instead of some of the other
> > structures we use for tracking.
>
> I don't think pKVM should hijack the xarray for other purposes.  At best, it will
> be confusing, at worst we'll end up with a mess if ARM ever supports the "generic"
> implementation.

Definitely wasn't referring to hijacking it for other purposes, which
is the main reason I wanted to clarify the documentation and the
naming of private_fd. Anyway, I'm glad to see that we're in agreement.
Once I've tightened the screws, I'll share the pKVM port as an RFC as
well.

Cheers,
/fuad