Re: [Xen-devel] [PATCH v3 08/14] x86/cpuid: Handle leaf 0x80000008 in guest_cpuid()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.01.17 at 17:30, <andrew.cooper3@xxxxxxxxxx> wrote:
> The entirety of edx is reserved.
> 
> Intel only defines the lower 16 bits of eax, although ebx is covered by the
> featureset ABI, so left unclobbered.
> 
> AMD uses 24 bits in eax, although nothing thus far has ever exposed a non-zero
> guest maxphysaddr to HVM guests.  Its semantics are not clearly expressed, so
> it is explicitly clobbered.  ecx contains some reserved bits, and several
> pieces of static topology information, which are left as the toolstack
> chooses.
> 
> A side effect of the common recalculation of maxlinaddr is that 32bit PV
> guests see a maximum linear address of 32, which is consistent with the hiding
> of other long mode information from them.
> 
> Finally, the call to guest_cpuid() in mtrr_var_range_msr_set() (introduced in
> c/s fff8160a) can be dropped, now that maxphysaddr can be read straight out of
> the cpuid_policy block.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>



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