Re: [Xen-devel] [PATCH v5 21/21] tools/libxc: Calculate xstate cpuid leaf from guest information

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Apr 07, 2016 at 12:57:26PM +0100, Andrew Cooper wrote:
> The existing logic is broken for heterogeneous migration.  By always
> advertising the host maximum xstate, a migration to a less capable host always
> fails as Xen cannot accomodate the xcr0_accum in the migration stream.
> 
> By calculating xstate from the feature information (which a multi-host
> toolstack will have levelled appropriately), the guest will have the current
> hosts maximum xstate advertised, allowing for correct migration to less
> capable hosts.
> 
> In addition, some further improvements and corrections:
>  - don't discard the known flags in sub-leaves 2..63 ECX
>  - zap sub-leaves beyond 62
>  - zap all bits in leaf 1, EBX/ECX.  No XSS features are currently supported.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Since this is mostly x86 code and signed off by two x86 maintainers, I'm
just rubber-stamping this patch:

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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