Re: [Xen-devel] [RFC PATCH 1/8] x86/domctl: introduce a pair of hypercall to set and get cpu topology

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/01/18 04:01, Chao Gao wrote:
> Define interface, structures and hypercalls for toolstack to build
> cpu topology and for guest that will retrieve it [1].
> Two subop hypercalls introduced by this patch:
> XEN_DOMCTL_set_cpu_topology to define cpu topology information per domain
> and XENMEM_get_cpu_topology to retrieve cpu topology information.
>
> [1]: during guest creation, those information helps hvmloader to build ACPI.
>
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>

I'm sorry, but this going in the wrong direction.  Details like this
should be contained and communicated exclusively in the CPUID policy.

Before the spectre/meltdown fire started, I had a prototype series
introducing a toolstack interface for getting and setting a full CPUID
policy at once, rather than piecewise.  I will be continuing with this
work once the dust settles.

In particular, we should not have multiple ways of conveying the same
information, or duplication of the same data inside the hypervisor.

If you rearrange your series to put the struct cpuid_policy changes
first, then patch 2 will become far more simple.  HVMLoader should
derive its topology information from the CPUID instruction, just as is
expected on native hardware.

~Andrew

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