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

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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@xxxxxxxxxx>
> > > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@xxxxxxxxxx/
> > > ---
> > >   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.



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