Re: [Xen-devel] Save paused cpu ctx

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.09.18 at 11:19, <aisaila@xxxxxxxxxxxxxxx> wrote:
> On Wed, 2018-09-19 at 03:01 -0600, Jan Beulich wrote:
>> > > > On 19.09.18 at 10:21, <aisaila@xxxxxxxxxxxxxxx> wrote:
>> > 
>> > I want to restart the discussion on dropping the "if ( v-
>> > >pause_flags &
>> > VPF_down )" from hvm_save_cpu_ctxt() and be able to save context in
>> > a
>> > vcup down state. The content of the ctx could be filled like it is
>> > described in Intel SDM, "9.1.1 Processor State After Reset" (https:
>> > //so 
>> > ftware.intel.com/sites/default/files/managed/39/c5/325462-sdm-vol-
>> > 1-
>> > 2abcd-3abcd.pdf   page 2996).
>> > 
>> > Is this enough to be up streamed?
>> 
>> Along the lines of what Roger has said - without knowing _why_ you
>> want to do that, it's hard to tell. It's pretty clear I think that we
>> don't
>> want to outright drop the condition, the question is just whether to
>> somewhat relax it for your purposes.
>> 
>> I'm afraid I also don't agree with your assertion that a down vCPU is
>> in "after reset" state: To me, such a vCPU could legitimately be
>> considered to be in that state, in the state it was in when it went
>> down, or in basically any other (perhaps random) state.
> 
> Processor State After Reset is just the name of the table in the
> manual. Having a default state to return on a query was the start point
> of the discussion. You are right, we can return whatever state the cpu
> was in before it went down. The code works fine like that, further
> more, this will make us have a smaller patch plus a legitimate ctx at
> the end of the query.

You didn't understand my response then: There is no "the state" for
a vCPU which is down. Therefore we shouldn't arbitrarily pick one of
the almost infinite number of options.

Also in your reply to Roger you didn't respond at all to the size
growth your proposed change would have for the migration stream,
as pointed out by him.

In any event - for now I continue to think that the code should
remain as is, and the caller should know whether (and _how_) to
deal with down vCPU-s.

>> Finally (and I'm sorry for being picky here) - why was this inquiry
>> addressed _To_ me instead of the list?
> 
> It was addressed to you because in v17 of the save_one series you said
> that we have to continue the discussion in a different thread. 

"We" is the community here, not just you and me.

Jan



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