Re: [Xen-devel] Deprecating HVM_PARAM_PAE_ENABLED

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.07.18 at 18:54, <andrew.cooper3@xxxxxxxxxx> wrote:
> The parameter was introduced in e661d66f51 (2006) and used in Xen, but
> removed from the hypervisor in c/s 5f14a87ce (2008) when CPUID
> calculations where moved from the hypervisor into libxc.
> 
> However, the field has always been propagated in the migration stream. 
> AFAICT, the only use for the HVM_PARAM is as a function parameter to
> xc_cpuid_apply_policy(), which is a very very expensive way of passing a
> function parameter!
> 
> Another curiosity is that HVM and PVH guests treat the toplevel xl.cfg
> pae boolean differently.  HVM honour the request, while PVH blindly
> ignores it and sets it to true.  There is nothing wrong (in principle)
> with a PVH non-PAE guest, so the boolean should be honoured IMO.
> 
> A separate usability niggle is that there is no interlink between the
> toplevel pae boolean and passing some custom cpuid= configuration.  The
> latter appears to take priority but only due to the order in which libxl
> processes the data.
> 
> Does anyone see any reason to keep HVM_PARAM_PAE_ENABLED around?

Fundamentally - no. What is the plan to communicate the guest config
"pae=" value from libxl to libxc then?

Jan



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