Re: [PATCH] evtchn: make EVTCHNOP_reset suitable for kexec

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 25/07/14 17:09, Jan Beulich wrote:
>>>> On 25.07.14 at 17:48, <vkuznets@redhat.com> wrote:
>> @@ -954,8 +955,20 @@ static long evtchn_reset(evtchn_reset_t *r)
>>      if ( rc )
>>          goto out;
>>  
>> -    for ( i = 0; port_is_valid(d, i); i++ )
>> -        (void)__evtchn_close(d, i);
>> +    for ( i = 1; port_is_valid(d, i); i++ )
>> +    {
>> +        /*
>> +         * Leave all interdomain connections to Dom0 untouched as we need to
>> +         * preserve store/console channels.
>> +         */
>> +        chn = evtchn_from_port(d, i);
>> +        if ( chn->state != ECS_INTERDOMAIN ||
>> +             chn->u.interdomain.remote_dom->domain_id != 0 )
>> +            (void)__evtchn_close(d, i);
>> +    }
> You can't alter the behavior of an existing hypercall like this. Did
> you at all check why it closes all channels, i.e. for what purpose
> it got introduced?
>
> And apart from that blindly leaving all interdomain channels intact
> doesn't seem reasonable either.
>
> Jan
>

I agree with your comment regarding interdomain channels.

However, there absolutely nothing a domain can do to recover from a
closed xenstore or console connection, as it is state set up by the
toolstack at domain build time, rather than state set up during early boot.

Whatever the intention of this hypercall originally, I can't see how a
domain could possibly recover having used it.

~Andrew