Re: [Xen-devel] [PATCH V3 2/3] x86/mm: allocate logdirty_ranges for altp2ms

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 10/30/18 6:28 PM, Andrew Cooper wrote:
> On 30/10/18 16:22, Jan Beulich wrote:
>>>>> On 29.10.18 at 13:40, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> This patch is a pre-requisite for the one fixing VGA logdirty
>>> freezes when using altp2m. It only concerns itself with the
>>> ranges allocation / deallocation / initialization part.
>> But while looking (briefly only for now) over patch 3 I couldn't
>> see any sync-ing of the log-dirty ranges there either. Doesn't
>> this need doing either there or here, if you go the copy route?
>>
>>> @@ -2271,6 +2297,7 @@ void p2m_flush_altp2m(struct domain *d)
>>>      {
>>>          p2m_flush_table(d->arch.altp2m_p2m[i]);
>>>          /* Uninit and reinit ept to force TLB shootdown */
>>> +        p2m_free_logdirty(d->arch.altp2m_p2m[i]);
>>>          ept_p2m_uninit(d->arch.altp2m_p2m[i]);
>>>          ept_p2m_init(d->arch.altp2m_p2m[i]);
>>>          d->arch.altp2m_eptp[i] = mfn_x(INVALID_MFN);
>>> @@ -2341,6 +2385,7 @@ int p2m_destroy_altp2m_by_id(struct domain *d, 
>>> unsigned int idx)
>>>          {
>>>              p2m_flush_table(d->arch.altp2m_p2m[idx]);
>>>              /* Uninit and reinit ept to force TLB shootdown */
>>> +            p2m_free_logdirty(d->arch.altp2m_p2m[idx]);
>>>              ept_p2m_uninit(d->arch.altp2m_p2m[idx]);
>>>              ept_p2m_init(d->arch.altp2m_p2m[idx]);
>>>              d->arch.altp2m_eptp[idx] = mfn_x(INVALID_MFN);
>>> @@ -2471,6 +2516,7 @@ static void p2m_reset_altp2m(struct p2m_domain *p2m)
>>>  {
>>>      p2m_flush_table(p2m);
>>>      /* Uninit and reinit ept to force TLB shootdown */
>>> +    p2m_free_logdirty(p2m);
>>>      ept_p2m_uninit(p2m);
>>>      ept_p2m_init(p2m);
>>>      p2m->min_remapped_gfn = gfn_x(INVALID_GFN);
>> For one these look all pretty similar, so I wonder why there's
>> no helper function. But that's not something you need to change.
>> Yet why are you freeing the log-dirty ranges here? These aren't
>> full cleanup paths afaict.
> 
> Rangesets get added to the domain rangeset list, and we clean them all
> up rangeset_domain_destroy()
> 
> TBH, I'm not sure why we do it like this, and I'm not 100% convinced it
> is a clever deallocation scheme.

To eliminate any confusion: are you saying that rangesets should only be
allocated, and never explicitly deallocated (since
rangeset_domain_destroy() takes care of that)? If that is correct, then
there's a problem in the code now with the way we're handling the
logdirty_ranges for the hostp2m (where we clean it up in p2m_free_one()
and p2m_teardown_hostp2m()).


Thanks,
Razvan

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