Re: [Xen-devel] [PATCH v2 07/25] arm/altp2m: Add altp2m init/teardown routines.

[Sergej Proskurin <proskurin@xxxxxxxxxxxxx>]

Hi Julien,


On 08/05/2016 11:20 AM, Julien Grall wrote:
> On 05/08/16 07:53, Sergej Proskurin wrote:
>> Hi Julien,
>
> Hello Sergej,
>
>> On 08/03/2016 08:12 PM, Julien Grall wrote:
>>> On 01/08/16 18:10, Sergej Proskurin wrote:
>>>> +int altp2m_init(struct domain *d)
>>>> +{
>>>> +    unsigned int i;
>>>> +
>>>> +    spin_lock_init(&d->arch.altp2m_lock);
>>>> +
>>>> +    for ( i = 0; i < MAX_ALTP2M; i++ )
>>>> +    {
>>>> +        d->arch.altp2m_p2m[i] = NULL;
>>>> +        d->arch.altp2m_vttbr[i] = INVALID_VTTBR;
>>>
>>> I don't think altp2m_vttbr is useful. There is no real performance
>>> impact to free the whole altp2m if the altp2m is destroyed (see
>>> altp2m_destroy_by_id) and re-allocated afterwards.
>>>
>>> The code will actually much simpler. With this solution you will be
>>> able to detect if an altp2m is available by testin altp2m_p2m[i] is
>>> NULL.
>>>
>>
>> This is true. I did not want to free the entire domain got every time
>> the hostp2m got changed, while altp2m was active (see
>> altp2m_propagate_change). But it would not introduce much more overhead
>> when it does. Thank you.
>
> I think you misunderstood my point. When you flush the altp2m you only
> need to reset lowest_mapped_gfn and max_mapped_gfn aside freeing
> intermediate page table.
>

I see your point. I will consider your suggestion in the next patch.
Thank you.

> The altp2m should be fully freed when it get destroyed, nobody will
> use it anyway. This will also simplify a lot the logic.

Best regards,
~Sergej


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