[PATCH 3/5] iommu/arm-smmu-v3: add IOMMU_CAP_BYPASS to the ARM SMMUv3 driver
From: robin.murphy@arm.com (Robin Murphy)
Date: 2017-07-19 11:00:59
Also in:
kvm, linux-iommu, lkml
On 19/07/17 10:33, Anup Patel wrote:
quoted hunk ↗ jump to hunk
The ARM SMMUv3 support bypassing transactions for which domain is not configured. The patch adds corresponding IOMMU capability to advertise this fact. Signed-off-by: Anup Patel <redacted> --- drivers/iommu/arm-smmu-v3.c | 2 ++ 1 file changed, 2 insertions(+)diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c index 568c400..a6c7f66 100644 --- a/drivers/iommu/arm-smmu-v3.c +++ b/drivers/iommu/arm-smmu-v3.c@@ -1423,6 +1423,8 @@ static bool arm_smmu_capable(enum iommu_cap cap) return true; case IOMMU_CAP_NOEXEC: return true; + case IOMMU_CAP_BYPASS: + return true;
And this is never true. If Linux knows a device masters through the SMMU, it will always have a default domain of some sort (either identity or DMA ops). If Linux doesn't know, then it won't have been able to initialise the stream table for the relevant stream IDs, thus any 'bypass' DMA is going to raise C_BAD_STE. SMMUv3 can effectively only bypass unknown stream IDs if disabled entirely. Robin.
default: return false; }