Hi Robin, On 04/22/2016 01:31 PM, Robin Murphy wrote: > 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?
sorry I understood you wanted to use IOMMU_CAP_INTR_REMAP as the sole criteria to detect whether MSI mapping was requested. > > 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)) But Can't we imagine a mix of smmus on the same platform, some requesting MSI mapping and some which don't. As soon as an smmu requires MSI mapping, CONFIG_IOMMU_DMA_RESERVED is set and acquire_msi_remapping_resources(domain) will be implemented & succeed. Doesn't it lead to a wrong decision. Do I miss something, or do you consider this situation as far-fetched? Thanks Eric > 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.bhus...@freescale.com> >>>> Signed-off-by: Eric Auger <eric.au...@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, >>>> }; >>>> >>>> >>> >> >