linux-kernel - Re: [PATCH v5 00/13] KVM: mm: fd-based approach for supporting KVM guest private memory

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Date:   Tue, 29 Mar 2022 00:04:16 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Nakajima, Jun" <jun.nakajima@...el.com>
Cc:     "Lutomirski, Andy" <luto@...nel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "qemu-devel@...gnu.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" <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>,
        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>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "david@...hat.com" <david@...hat.com>
Subject: Re: [PATCH v5 00/13] KVM: mm: fd-based approach for supporting KVM
 guest private memory

On Mon, Mar 28, 2022, Nakajima, Jun wrote:
> > On Mar 28, 2022, at 1:16 PM, Andy Lutomirski <luto@...nel.org> wrote:
> > 
> > On Thu, Mar 10, 2022 at 6:09 AM Chao Peng <chao.p.peng@...ux.intel.com> wrote:
> >> 
> >> This is the v5 of this series which tries to implement the fd-based KVM
> >> guest private memory. The patches are based on latest kvm/queue branch
> >> commit:
> >> 
> >>  d5089416b7fb KVM: x86: Introduce KVM_CAP_DISABLE_QUIRKS2
> > 
> > Can this series be run and a VM booted without TDX?  A feature like
> > that might help push it forward.
> > 
> > —Andy
> 
> Since the userspace VMM (e.g. QEMU) loses direct access to private memory of
> the VM, the guest needs to avoid using the private memory for (virtual) DMA
> buffers, for example. Otherwise, it would need to use bounce buffers, i.e. we
> would need changes to the VM. I think we can try that (i.e. add only bounce
> buffer changes). What do you think?

I would love to be able to test this series and run full-blown VMs without TDX or
SEV hardware.

The other option for getting test coverage is KVM selftests, which don't have an
existing guest that needs to be enlightened.  Vishal is doing work on that front,
though I think it's still in early stages.  Long term, selftests will also be great
for negative testing.