linux-kernel - Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

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Message-ID: <Y8bZ/J98V5i3wG/v@google.com>
Date:   Tue, 17 Jan 2023 17:25:16 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     Binbin Wu <binbin.wu@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-arch@...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>,
        Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, 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>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

On Tue, Jan 17, 2023, Chao Peng wrote:
> On Tue, Jan 17, 2023 at 11:21:10AM +0800, Binbin Wu wrote:
> > 
> > On 12/2/2022 2:13 PM, Chao Peng wrote:
> > > In confidential computing usages, whether a page is private or shared is
> > > necessary information for KVM to perform operations like page fault
> > > handling, page zapping etc. There are other potential use cases for
> > > per-page memory attributes, e.g. to make memory read-only (or no-exec,
> > > or exec-only, etc.) without having to modify memslots.
> > > 
> > > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> > > userspace to operate on the per-page memory attributes.
> > >    - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
> > >      a guest memory range.
> > >    - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
> > >      memory attributes.
> > > 
> > > KVM internally uses xarray to store the per-page memory attributes.
> > > 
> > > Suggested-by: Sean Christopherson <seanjc@...gle.com>
> > > Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> > > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> > > ---
> > >   Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
> > >   arch/x86/kvm/Kconfig           |  1 +
> > >   include/linux/kvm_host.h       |  3 ++
> > >   include/uapi/linux/kvm.h       | 17 ++++++++
> > 
> > Should the changes introduced in this file also need to be added in
> > tools/include/uapi/linux/kvm.h ?
> 
> Yes I think.

I'm not sure how Paolo or others feel, but my preference is to never update KVM's
uapi headers in tools/ in KVM's tree.  Nothing KVM-related in tools/ actually
relies on the headers being copied into tools/, e.g. KVM selftests pulls KVM's
headers from the .../usr/include/ directory that's populated by `make headers_install`.

Perf's tooling is what actually "needs" the headers to be copied into tools/, so
my preference is to let the tools/perf maintainers deal with the headache of keeping
everything up-to-date.

> But I'm hesitate to include in this patch or not. I see many commits sync
> kernel kvm.h to tools's copy. Looks that is done periodically and with a
> 'pull' model.