Re: [PATCH] x86/PV: fix unintended dependency of m2p-strict mode on migration-v2

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

On 01/02/16 16:28, Jan Beulich wrote:
>>>> On 01.02.16 at 15:07, <andrew.cooper3@citrix.com> wrote:
>> On 01/02/16 13:20, Jan Beulich wrote:
>>> Ping? (I'd really like to get this resolved, so we don't need to
>>> indefinitely run with non-upstream behavior in our distros.)
>> My remaining issue is whether this loop gets executed by default.
>>
>> I realise that there is a difference between legacy and v2 migration,
>> and that v2 migration by default worked.  If that means we managed to
>> skip this loop in its entirety for v2, then I am far less concerned
>> about the overhead.
> But had been there before: Of course we could skip the loop if
> the bit in d->vm_assist doesn't change. But as expressed before,
> with you having already indicated that perhaps it would be better
> to have v2 migration do the relevant operations in the other (v1)
> order, the moment that was actually done the benefit of avoiding
> the loop would be gone.
>
> To be clear - if rendering the code dead (which is what you ask
> for) until v2 migration happens to get changed is the only way to
> get this code in, I will submit a v2 with that extra conditional.

Migration v2 currently loads vcpu context before pinning the pagetables,
which means that the vm_assist should get set up properly, before L4
tables are processed.

It was my understanding that this is the correct way around, and
m2p-strict mode only broke when you backported it to migration v1 systems?

~Andrew