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SubjectRe: [RFC] CPUID usage for interaction between Hypervisors and Linux.
Jeremy Fitzhardinge wrote:
> Alok Kataria wrote:
>
> No, we're not getting anywhere. This is an outright broken idea. The
> space is too small to be able to chop up in this way, and the number of
> vendors too large to be able to do it without having a central oversight.
>
> The only way this can work is by having explicit positive identification
> of each group of leaves with a signature. If there's a recognizable
> signature, then you can inspect the rest of the group; if not, then you
> can't. That way, you can avoid any leaf usage which doesn't conform to
> this model, and you can also simultaneously support multiple hypervisor
> ABIs. It also accommodates existing hypervisor use of this leaf space,
> even if they currently use a fixed location within it.
>
> A concrete counter-proposal:

Mmm, cpuid bikeshedding :-)

> The space 0x40000000-0x400000ff is reserved for hypervisor usage.
>
> This region is divided into 16 16-leaf blocks. Each block has the
> structure:
>
> 0x400000x0:
> eax: max used leaf within the leaf block (max 0x400000xf)

Why even bother with this? It doesn't seem necessary in your proposal.

Regards,

Anthony Liguori


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