From adf5e5168bd51c42332ebaa709351fa6ed65ea73 Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Fri, 27 Jan 2017 12:22:54 +0000 Subject: [PATCH] iommu: Better document the IOMMU_PRIV flag This is a fairly subtle thing - let's make sure it's described as clearly as possible to avoid potential misunderstandings. Signed-off-by: Robin Murphy Signed-off-by: Will Deacon --- include/linux/iommu.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/include/linux/iommu.h b/include/linux/iommu.h index 2e4de0deee53..88ec8c6580d3 100644 --- a/include/linux/iommu.h +++ b/include/linux/iommu.h @@ -32,10 +32,13 @@ #define IOMMU_NOEXEC (1 << 3) #define IOMMU_MMIO (1 << 4) /* e.g. things like MSI doorbells */ /* - * This is to make the IOMMU API setup privileged - * mapppings accessible by the master only at higher - * privileged execution level and inaccessible at - * less privileged levels. + * Where the bus hardware includes a privilege level as part of its access type + * markings, and certain devices are capable of issuing transactions marked as + * either 'supervisor' or 'user', the IOMMU_PRIV flag requests that the other + * given permission flags only apply to accesses at the higher privilege level, + * and that unprivileged transactions should have as little access as possible. + * This would usually imply the same permissions as kernel mappings on the CPU, + * if the IOMMU page table format is equivalent. */ #define IOMMU_PRIV (1 << 5) -- 2.20.1