Re: [Xen-devel] [PATCH] xen: reset creation_finished flag on soft reset

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

Andrew Cooper <andrew.cooper3@xxxxxxxxxx> writes:

> On 01/09/2017 10:11, Vitaly Kuznetsov wrote:
>> C/s e7dabe5 ("x86/hvm: don't unconditionally create a default ioreq
>> server") broke soft reset when QEMU traditional is being used. During
>> soft reset QEMU is relaunched and default ioreq server needs to be
>> re-created upon first HVM_PARAM_*IOREQ_* request. The flag will be
>> set back to 'true' when toolstack unpauses the domain, just like after
>> normal creation.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>
> Sorry, but nack.  d->creation_finished is used for a number of things,
> one being TLB safety before the vcpus have started executing.
>
> We either need to split the variable, or rework e7dabe5 to not use this.
>

I think that adding another flag is a bad idea, even 'creation_finished'
flag looks a bit hackish to me. Adjusting e7dabe5 is probably
better. However, while reading its blurb I don't fully understand the
change: on migration we create new domain and thus reset
creation_finished. During QEMU launch we still need to create ioreq
server. Paul, could you please elaborate a bit (e.g. what are we
guarding against, when creating ioreq server is redundant) so we can
suggest a fix for soft reset? 

Thanks, 

-- 
  Vitaly

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