Re: [Xen-devel] mem_sharing_nominate_page: p2mt should never change before p2m_change_type()

[Nai Xia <nai.xia@xxxxxxxxx>]

Thanks. Please append the following line to the change log:
Signed-off-by: Nai Xia <nai.xia@xxxxxxxxx>

BR,
Nai Xia

On 2013å08æ06æ 23:38, Andres Lagar-Cavilla wrote:
>> The p2mt change check for p2m_change_type() was first introduced when this 
>> code path was not protected by p2m_lock().
>> Now this code path is protected by p2m_lock. So p2mt should never change 
>> before p2m_change_type().
> 
> Makes sense. You need to put a proper Signed-off-by line. In any case:
> Acked-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
> 
> Andres
>>
>> ---
>> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
>> index 0364bb0..b3940cb 100644
>> --- a/xen/arch/x86/mm/mem_sharing.c
>> +++ b/xen/arch/x86/mm/mem_sharing.c
>> @@ -900,20 +900,8 @@ int mem_sharing_nominate_page(struct domain *d,
>>         goto out;
>>     }
>>
>> -    /* Change the p2m type */
>> -    if ( p2m_change_type(d, gfn, p2mt, p2m_ram_shared) != p2mt )
>> -    {
>> -        /* This is unlikely, as the type must have changed since we've 
>> checked
>> -         * it a few lines above.
>> -         * The mfn needs to revert back to rw type. This should never fail,
>> -         * since no-one knew that the mfn was temporarily sharable */
>> -        mem_sharing_gfn_destroy(page, d, gfn_info);
>> -        xfree(page->sharing);
>> -        page->sharing = NULL;
>> -        /* NOTE: We haven't yet added this to the audit list. */
>> -        BUG_ON(page_make_private(d, page) != 0);
>> -        goto out;
>> -    }
>> +    /* Change the p2m type, should never fail with p2m locked. */
>> +    BUG_ON(p2m_change_type(d, gfn, p2mt, p2m_ram_shared) != p2mt);
>>
>>     /* Account for this page. */
>>     atomic_inc(&nr_shared_mfns);
>>
>>
>>
>

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