Re: [Qemu-devel] [PATCH v4 2/3] target-i386: add migration support for Intel LMCE

[Paolo Bonzini]

On 16/06/2016 19:36, Eduardo Habkost wrote:
>> > 
>> > Eduardo said nice for this part in previous version [1], so we may wait
>> > for his comments?
>> > 
>> > [1] http://lists.nongnu.org/archive/html/qemu-devel/2016-06/msg01992.html
> I agree we don't need this check, but I still believe it is a
> nice thing to have.
> 
> In addition to detecting user errors, they don't hurt and are
> useful for things like "-cpu host", that don't guarantee
> live-migration compatibility but still allow migration if you
> ensure host capabilities are the same on both sides.

On the other hand we don't check for this on any other property, either
CPU or device, do we?  Considering "lmce=on" always breaks on an old
kernel (i.e. there's no need for an explicit ",enforce" on the -cpu
flag), I think it's unnecessary and makes things inconsistent.

> (I was going to suggest enabling lmce automatically on "-cpu
> host" as a follow-up patch, BTW.)

Interesting.  Technically it comes from the host kernel, not from the
host CPU.  But it does sounds like a good idea; -cpu host pretty much
implies the same kernel (in addition to the same processor) on both
sides of the migration.

Paolo