From: Robin Murphy Date: Fri, 27 Jan 2017 12:22:54 +0000 (+0000) Subject: iommu: Better document the IOMMU_PRIV flag X-Git-Tag: v4.12-rc1~50^2^5~2^2~13 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=adf5e5168bd51c42332ebaa709351fa6ed65ea73;p=thirdparty%2Fkernel%2Flinux.git 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 --- diff --git a/include/linux/iommu.h b/include/linux/iommu.h index 2e4de0deee531..88ec8c6580d3f 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)