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Re: [Xen-devel] [PATCH] x86/mm: Improve ring management for memory events. Do not lose guest events

  • To: "Olaf Hering" <olaf@xxxxxxxxx>
  • From: "Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>
  • Date: Mon, 16 Jan 2012 07:08:16 -0800
  • Cc: andres@xxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, tim@xxxxxxx, Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>, adin@xxxxxxxxxxxxxx
  • Delivery-date: Mon, 16 Jan 2012 15:08:38 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

> On Wed, Jan 11, Andres Lagar-Cavilla wrote:
>> @@ -898,7 +902,7 @@ void p2m_mem_paging_drop_page(struct dom
>>   * already sent to the pager. In this case the caller has to try again
>> until the
>>   * gfn is fully paged in again.
>>   */
>> -void p2m_mem_paging_populate(struct domain *d, unsigned long gfn)
>> +int p2m_mem_paging_populate(struct domain *d, unsigned long gfn)
>>  {
>>      struct vcpu *v = current;
>>      mem_event_request_t req;
> What is the reason to return an error here? None of the callers need to
> check it because they already know their condition (which is
> p2m_is_paging()). And your patch doesnt seem to update them. Foreigners
> try again, requests from the target domain do currently also try again
> until my change to use wait queues in gfn_to_mfn* is finished. And even
> then the call p2m_mem_paging_populate() will most likely remain a
> one-shot/must-succeed thing if the request is from the target domain.
> The only condition to care about in p2m_mem_paging_populate() is -ENOSYS
> from mem_event_claim_slot(), which your patch already handles by
> crashing the guest. Since the guest is in an kind-of undefined state
> anyway if the pager disappears while some gfns are still in paging state,
> this is one of the possible actions.

Ok, we'll make it void. Anything else pending?
> Olaf

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