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SubjectRe: [PATCH v7 01/10] iommu: Add DOMAIN_ATTR_MSI_MAPPING attribute
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On 20/04/16 16:58, Eric Auger wrote:
> Hi Robin,
> On 04/20/2016 02:47 PM, Robin Murphy wrote:
>> Hi Eric,
>>
>> On 19/04/16 17:56, Eric Auger wrote:
>>> Introduce a new DOMAIN_ATTR_MSI_MAPPING domain attribute. If supported,
>>> this means the MSI addresses need to be mapped in the IOMMU.
>>>
>>> x86 IOMMUs typically don't expose the attribute since on x86, MSI write
>>> transaction addresses always are within the 1MB PA region [FEE0_0000h -
>>> FEF0_000h] window which directly targets the APIC configuration space and
>>> hence bypass the sMMU. On ARM and PowerPC however MSI transactions are
>>> conveyed through the IOMMU.
>>
>> What's stopping us from simply inferring this from the domain's IOMMU
>> not advertising interrupt remapping capabilities?
> My current understanding is it is not possible:
> on x86 CAP_INTR_REMAP is not systematically exposed (the feature can be
> disabled) and MSIs are never mapped in the IOMMU I think.

Not sure I follow - if the feature is disabled such that the IOMMU
doesn't isolate MSIs, then it's no different a situation from the SMMU, no?

My point was that this logic:

if (IOMMU_CAP_INTR_REMAP)
we're good
else if (DOMAIN_ATTR_MSI_MAPPING)
if (acquire_msi_remapping_resources(domain))
we're good
else
oh no!
else
oh no!

should be easily reducible to this:

if (IOMMU_CAP_INTR_REMAP)
we're good
else if (acquire_msi_remapping_resources(domain))
we're good
else
oh no! // Don't care whether the domain ran out of
// resources or simply doesn't support it,
// either way we can't proceed.

Robin.

> Best Regards
>
> Eric
>>
>> Robin.
>>
>>> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
>>> Signed-off-by: Eric Auger <eric.auger@linaro.org>
>>>
>>> ---
>>>
>>> v4 -> v5:
>>> - introduce the user in the next patch
>>>
>>> RFC v1 -> v1:
>>> - the data field is not used
>>> - for this attribute domain_get_attr simply returns 0 if the MSI_MAPPING
>>> capability if needed or <0 if not.
>>> - removed struct iommu_domain_msi_maps
>>> ---
>>> include/linux/iommu.h | 1 +
>>> 1 file changed, 1 insertion(+)
>>>
>>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>>> index 62a5eae..b3e8c5b 100644
>>> --- a/include/linux/iommu.h
>>> +++ b/include/linux/iommu.h
>>> @@ -113,6 +113,7 @@ enum iommu_attr {
>>> DOMAIN_ATTR_FSL_PAMU_ENABLE,
>>> DOMAIN_ATTR_FSL_PAMUV1,
>>> DOMAIN_ATTR_NESTING, /* two stages of translation */
>>> + DOMAIN_ATTR_MSI_MAPPING, /* Require MSIs mapping in iommu */
>>> DOMAIN_ATTR_MAX,
>>> };
>>>
>>>
>>
>

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