Re: [PATCH 3/8] xen/arm: Implement p2m_type_t as an enum

["Egger, Christoph" <chegger@amazon.de>]

On 05.12.13 16:56, Ian Campbell wrote:
> On Thu, 2013-12-05 at 16:51 +0100, Egger, Christoph wrote:
>> On 05.12.13 16:42, Julien Grall wrote:
>>> Until now, Xen doesn't know the type of the page (ram, foreign page, mmio,...).
>>> Introduce p2m_type_t with basic types:
>>>     - p2m_invalid: Nothing is mapped here
>>>     - p2m_ram_rw: Normal read/write guest RAM
>>>     - p2m_ram_ro: Read-only guest RAM
>>>     - p2m_mmio_direct: Read/write mapping of device memory
>>>     - p2m_map_foreign: RAM page from foreign guest
>>>
>>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>>> ---
>>>  xen/include/asm-arm/p2m.h |   13 ++++++++++---
>>>  1 file changed, 10 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
>>> index f079f00..b24f94a 100644
>>> --- a/xen/include/asm-arm/p2m.h
>>> +++ b/xen/include/asm-arm/p2m.h
>>> @@ -20,6 +20,16 @@ struct p2m_domain {
>>>      uint8_t vmid;
>>>  };
>>>  
>>> +typedef enum {
>>> +    p2m_invalid = 0,        /* Nothing mapped here */
>>> +    p2m_ram_rw = 1,         /* Normal read/write guest RAM */
>>> +    p2m_ram_ro = 2,         /* Read-only; writes are silently dropped */
>>> +    p2m_mmio_direct = 3,    /* Read/write mapping of genuine MMIO area */
>>> +    p2m_map_foreign = 4,    /* Ram pages from foreign domain */
>>> +} p2m_type_t;
>>> +
>>> +#define p2m_is_foreign(_t) ((_t) == p2m_map_foreign)
>>> +
>>
>> Is it possible to merge p2m_type_t with x86 and move into common code?
> 
> Not really, the p2m handling is very different on the two arches, even
> if they look superficially similar at this level.

That does not imply there is no common logic from the algorithm POV.
Do you see a way split the algorithm into architecture-specific and
architecture-independent parts?

> x86 has more types than can fit in the available pte space on ARM for a
> start.
>
> I'd like to keep them separate please.

Ok. Then leave the declaration in the architecture specific part
and make the accessors available for the common code.
In OO-languages this is called an 'interface'.

Christoph