Re: [PATCH v9 4/5] x86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

[Yu Zhang <yu.c.zhang@linux.intel.com>]

On 3/24/2017 6:37 PM, Jan Beulich wrote:
>>>> On 24.03.17 at 10:05, <yu.c.zhang@linux.intel.com> wrote:
>> On 3/23/2017 5:00 PM, Jan Beulich wrote:
>>>>>> On 23.03.17 at 04:23, <yu.c.zhang@linux.intel.com> wrote:
>>>> On 3/22/2017 10:29 PM, Jan Beulich wrote:
>>>>>>>> On 21.03.17 at 03:52, <yu.c.zhang@linux.intel.com> wrote:
>>>>>> --- a/xen/arch/x86/hvm/ioreq.c
>>>>>> +++ b/xen/arch/x86/hvm/ioreq.c
>>>>>> @@ -949,6 +949,14 @@ int hvm_map_mem_type_to_ioreq_server(struct domain *d,
>> ioservid_t id,
>>>>>>     
>>>>>>         spin_unlock_recursive(&d->arch.hvm_domain.ioreq_server.lock);
>>>>>>     
>>>>>> +    if ( rc == 0 && flags == 0 )
>>>>>> +    {
>>>>>> +        struct p2m_domain *p2m = p2m_get_hostp2m(d);
>>>>>> +
>>>>>> +        if ( read_atomic(&p2m->ioreq.entry_count) )
>>>>>> +            p2m_change_entry_type_global(d, p2m_ioreq_server, p2m_ram_rw);
>>>>>> +    }
>>>>> If you do this after dropping the lock, don't you risk a race with
>>>>> another server mapping the type to itself?
>>>> I believe it's OK. Remaining p2m_ioreq_server entries still needs to be
>>>> cleaned anyway.
>>> Are you refusing a new server mapping the type before being
>>> done with the cleanup?
>> No. I meant even a new server is mapped, we can still sweep the p2m
>> table later asynchronously.
>> But this reminds me other point - will a dm op be interrupted by another
>> one, or should it?
> Interrupted? Two of them may run in parallel on different CPUs,
> against the same target domain.

Right. That's possible.

>> Since we have patch 5/5 which sweep the p2m table right after the unmap
>> happens, maybe
>> we should refuse any mapping requirement if there's remaining
>> p2m_ioreq_server entries.
> That's what I've tried to hint at with my question.

Oh. I see. Thank you, Jan. :-)

Yu
> Jan
>
>
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