Re: [PATCH v5 10/17] xen/arm: map_regions_rw_cache: Map the region with p2m->default_access

[Julien Grall <julien.grall@arm.com>]

On 06/07/16 12:22, Julien Grall wrote:
>
>
> On 06/07/16 12:17, Stefano Stabellini wrote:
>> On Wed, 6 Jul 2016, Julien Grall wrote:
>>> (CC Tamas)
>>>
>>> On 06/07/16 11:43, Stefano Stabellini wrote:
>>>> On Tue, 28 Jun 2016, Julien Grall wrote:
>>>>> The parameter 'access' is used by memaccess to restrict temporarily
>>>>> the
>>>>> permission. This parameter should not be used for other purpose (such
>>>>> as restricting permanently the permission).
>>>>>
>>>>> The type p2m_mmio_direct will map the region Read-Write and
>>>>> non-executable. Note that this is already the current behavior with
>>>>> the
>>>>> combination of the type and the access. So there is no functional
>>>>> change.
>>>>>
>>>>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>>>>
>>>> I could be mistaken, but isn't default_access actually p2m_access_rwx?
>>>
>>> By default, the access is p2m_access_rwx. However this can be changed by
>>> memaccess and the new default value is stored in
>>> arch->p2m.default_access. I
>>> have CCed Tamas to confirm that.
>>>
>>> Note that this is how the other calls are done.
>>
>> This patch replaces p2m_access_rw with default_access, which is
>> p2m_access_rwx by default. Is it actually indended?
>
> Yes, I explained why in the commit message.
>
> "The type p2m_mmio_direct will map the region Read-Write and
> non-executable. Note that this is already the current behavior with the
> combination of the type and the access. So there is no functional
> change."

Thinking a bit more, I will reword the commit message with:

"The parameter 'access' used by memaccess to restrict temporarily the 
permission. This parameter should not be for other purpose (such as 
restricting permanently the permission).

Instead, we should use the default_access provided by memaccess. When it 
is not enabled, the access will be p2m_access_rwx (i.e no restriction 
applied).

The type p2m_mmio_direct will map the region read-write and 
non-executable before any further restriction by memaccess. note that 
this is already the current behavior with the combination of the type 
and the access. So there is no functional change".

Regards,

-- 
Julien Grall

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