[Xen-devel] Re: [RFC PATCH 18/33] Subarch support for CPUID instruction

[Arjan van de Ven <arjan@xxxxxxxxxxxxx>]

On Tue, 2006-07-18 at 00:00 -0700, Chris Wright wrote:
> plain text document attachment (i386-cpuid)
> Allow subarchitectures to modify the CPUID instruction.  This allows
> the subarch to provide a limited set of CPUID feature flags during CPU
> identification.  Add a subarch implementation for Xen that traps to the
> hypervisor where unsupported feature flags can be hidden from guests.

Hi,

I'm wondering if this is entirely the wrong level of abstraction; to me
it feels the subarch shouldn't override the actual cpuid, but the cpu
feature flags that linux uses. That's a lot less messy: cpuid has many
many pieces of information which are near impossible to filter in
practice, however filtering the USAGE of it is trivial; linux basically
flattens the cpuid namespace into a simple bitmap of "what the kernel
can use". That is really what the subarch should filter/fixup, just like
we do for cpu quirks etc etc.

Greetings,
   Arjan van de Ven


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