Re: [Xen-devel] [PATCH] arm/p2m: Fix regression during domain shutdown with active mem_access

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

On Tue, Jan 24, 2017 at 3:13 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> Hi Tamas,
>
> On 24/01/2017 22:10, Tamas K Lengyel wrote:
>>
>> The change in commit 438c5fe4f0c introduced a regression for domains where
>> mem_acces is or was active. When relinquish_p2m_mapping attempts to clear
>> a page where the order is not 0 the following ASSERT is triggered:
>>
>>     ASSERT(!p2m->mem_access_enabled || page_order == 0);
>>
>> This regression was unfortunately not caught during testing in preparation
>> for the 4.8 release.
>>
>> As at this point during domain shutdown it is safe to skip mem_access
>> paths
>> altogether (pages are being relinquished), this patch flips the
>> mem_access_enabled flag to forgo any radix-tree lookups and to avoid
>> tripping the ASSERT.
>>
>> Ideally this fix would be part of Xen 4.8.1.
>
>
> How about fixing the ASSERT rather than turning-off memaccess crudely?
>
> For instance by whether whether the domain is dying.
>

We can do that too if preferred. This way though we also shortcut all
calls to p2m_mem_access_radix_set, so shutdown would be faster.

Tamas

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