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Date: Fri, 22 Apr 2016 12:31:04 +0100 From: Robin Murphy <robin.murphy@....com> To: Eric Auger <eric.auger@...aro.org>, eric.auger@...com, alex.williamson@...hat.com, will.deacon@....com, joro@...tes.org, tglx@...utronix.de, jason@...edaemon.net, marc.zyngier@....com, christoffer.dall@...aro.org, linux-arm-kernel@...ts.infradead.org Cc: patches@...aro.org, linux-kernel@...r.kernel.org, Bharat.Bhushan@...escale.com, pranav.sawargaonkar@...il.com, p.fedin@...sung.com, iommu@...ts.linux-foundation.org, Jean-Philippe.Brucker@....com, julien.grall@....com Subject: Re: [PATCH v7 01/10] iommu: Add DOMAIN_ATTR_MSI_MAPPING attribute 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@...escale.com> >>> Signed-off-by: Eric Auger <eric.auger@...aro.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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