Re: [PATCH v2 1/2] xen: introduce arch_iommu_grant_(un)map_page

[Julien Grall <julien.grall@linaro.org>]

On 24/07/14 12:16, Stefano Stabellini wrote:
> On Thu, 24 Jul 2014, Julien Grall wrote:
>> On 24/07/14 12:07, Stefano Stabellini wrote:
>>> On Thu, 24 Jul 2014, Julien Grall wrote:
>>>> Hi Stefano,
>>>>
>>>> The Title of the commit message is now wrong.
>>>
>>> Thanks, I didn't notice.
>>>
>>>
>>>> On 23/07/14 18:19, Stefano Stabellini wrote:
>>>>> Introduce two arch specific functions to create a new p2m mapping of
>>>>> granted pages at pfn == mfn.
>>>>> The x86 implementation just returns ENOSYS.
>>>>>
>>>>> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>>>>> ---
>>>>>     xen/arch/arm/p2m.c        |   19 +++++++++++++++++++
>>>>>     xen/include/asm-arm/p2m.h |    4 ++++
>>>>>     xen/include/asm-x86/p2m.h |   13 +++++++++++++
>>>>>     3 files changed, 36 insertions(+)
>>>>>
>>>>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>>>>> index 9960e17..c38af59 100644
>>>>> --- a/xen/arch/arm/p2m.c
>>>>> +++ b/xen/arch/arm/p2m.c
>>>>> @@ -555,6 +555,25 @@ void guest_physmap_remove_page(struct domain *d,
>>>>>                           pfn_to_paddr(mfn), MATTR_MEM, p2m_invalid);
>>>>>     }
>>>>>
>>>>> +int arch_grant_map_page_identity(struct domain *d, unsigned long frame,
>>>>> +                                 bool_t writeable)
>>>>> +{
>>>>> +    p2m_type_t t;
>>>>> +
>>>>> +    if ( writeable )
>>>>> +        t = p2m_ram_rw;
>>>>> +    else
>>>>> +        t = p2m_ram_ro;
>>>>
>>>> This is not the right p2m type to use here. p2m_ram_{rw,ro} allow foreign
>>>> mapping. So another guest could access to the grant.
>>>>
>>>> I would use p2m_iommu_map_{rw,ro}.
>>>
>>>
>>> I see. I'll make the change and add a comment to explain why we are
>>> using p2m_iommu types for non-iommu related mappings.
>>
>> The code to add the 1:1 mapping for the SMMU is very ugly. I was wondering if
>> we could drop the iommu_map_page callback and
>> directly use arch_grant_map_page_identity in all the case.
>>
>> It would avoid the if/else in the grant code.
>
> Thing is arch_grant_map_page_identity has nothing to do with IOMMUs. It
> gets confusing, especially on x86 where people don't know why we need
> this. The if/else is ugly but clearer.
> See also the previous email exchange with Jan.

Ok. So could we call this function from iommu_map_page on the SMMU? It 
would at least avoid duplicating the code?

Regards,

-- 
Julien Grall