Re: [Xen-devel] [PATCH v2 16/17] tools/libxc: Restore CPUID/MSR data found in the migration stream

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.01.2020 15:34, Andrew Cooper wrote:
> With all other pieces in place, it is now safe to restore the CPUID and MSR
> data in the migration stream, rather than discarding them and using the higher
> level toolstacks compatibility logic.
> 
> While this is a small patch, it has large implications for migrated/resumed
> domains.  Most obviously, the CPU family/model/stepping data,
> cache/tlb/etc. will no longer change behind the guests back.
> 
> Another change is the interpretation of the Xend cpuid strings.  The 'k'
> option is not a sensible thing to have ever supported, and 's' is how how the
> stream will end up behaving.

I'm a little confused I guess - I'd have expected such a description
to mean that ...

> --- a/tools/libxc/xc_cpuid_x86.c
> +++ b/tools/libxc/xc_cpuid_x86.c
> @@ -291,10 +291,9 @@ int xc_set_domain_cpu_policy(xc_interface *xch, uint32_t 
> domid,
>   *   '0' -> force to 0
>   *   'x' -> we don't care (use default)
>   *   'k' -> pass through host value
> - *   's' -> pass through the first time and then keep the same value
> - *          across save/restore and migration.
> + *   's' -> legacy alias for 'k'

... 's' remains documented as is, and 'k' to become a legacy alias.

Jan

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