[Intel IOMMU][patch 6/8] Doc updates for Intel Virtualization Technology for Directed I/O.

Ashok Raj
2007-04-24T15:13:46Z

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Document Intel IOMMU driver boot option.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Index: linux-2.6.21-rc5/Documentation/Intel-IOMMU.txt
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.21-rc5/Documentation/Intel-IOMMU.txt 2007-04-17 05:41:56.000000000 -0700
@@ -0,0 +1,119 @@
+Linux IOMMU Support
+===================
+
+The architecture spec can be obtained from the below location.
+
+http://www.intel.com/technology/virtualization/
+
+This guide gives a quick cheat sheet for some basic understanding.
+
+Some Keywords
+
+DMAR - DMA remapping
+DRHD - DMA Engine Reporting Structure
+RMRR - Reserved memory Region Reporting Structure
+ZLR - Zero length reads from PCI devices
+IOVA - IO Virtual address.
+
+Basic stuff
+-----------
+
+ACPI enumerates and lists the different DMA engines in the platform, and
+device scope relationships between PCI devices and which DMA engine controls
+them.
+
+What is RMRR?
+-------------
+
+There are some devices the BIOS controls, for e.g USB devices to perform
+PS2 emulation. The regions of memory used for these devices are marked
+reserved in the e820 map. When we turn on DMA translation, DMA to those
+regions will fail. Hence BIOS uses RMRR to specify these regions along with
+devices that need to access these regions. OS is expected to setup
+unity mappings for these regions for these devices to access these regions.
+
+How is IOVA generated?
+---------------------
+
+Well behaved drivers call pci_map_*() calls before sending command to device
+that needs to perform DMA. Once DMA is completed and mapping is no longer
+required, device performs a pci_unmap_*() calls to unmap the region.
+
+The Intel IOMMU driver allocates a virtual address per domain. Each PCIE
+device has its own domain (hence protection). Devices under p2p bridges
+share the virtual address with all devices under the p2p bridge due to
+transaction id aliasing for p2p bridges.
+
+IOVA generation is pretty generic. We used the same technique as vmalloc()
+but these are not global address spaces, but separate for each domain.
+Different DMA engines may support different number of domains.
+
+We also allocate gaurd pages with each mapping, so we can attempt to catch
+any overflow that might happen.
+
+
+Graphics Problems?
+------------------
+If you encounter issues with graphics devices, you can try adding
+option intel_iommu=igfx_off to turn off the integrated graphics engine.
+
+If it happens to be a PCI device included in the INCLUDE_ALL Engine,
+then try the intel_iommu=gfx_workaround to setup a 1-1 map. We hear
+graphics drivers may be in process of using DMA api's in the near
+future....
+
+Some exceptions to IOVA
+-----------------------
+Interrupt ranges are not address translated, (0xfee00000 - 0xfeefffff).
+The same is true for peer to peer transactions. Hence we reserve the
+address from PCI MMIO ranges so they are not allocated for IOVA addresses.
+
+
+Fault reporting
+---------------
+When errors are reported, the DMA engine signals via an interrupt. The fault
+reason and device that caused it with fault reason is printed on console.
+
+See below for sample.
+
+
+Boot Message Sample
+-------------------
+
+Something like this gets printed indicating presence of DMAR tables
+in ACPI.
+
+ACPI: DMAR (v001 A M I OEMDMAR 0x00000001 MSFT 0x00000097) @ 0x000000007f5b5ef0
+
+When DMAR is being processed and initialized by ACPI, prints DMAR locations
+and any RMRR's processed.
+
+ACPI DMAR:Host address width 36
+ACPI DMAR:DRHD (flags: 0x00000000)base: 0x00000000fed90000
+ACPI DMAR:DRHD (flags: 0x00000000)base: 0x00000000fed91000
+ACPI DMAR:DRHD (flags: 0x00000001)base: 0x00000000fed93000
+ACPI DMAR:RMRR base: 0x00000000000ed000 end: 0x00000000000effff
+ACPI DMAR:RMRR base: 0x000000007f600000 end: 0x000000007fffffff
+
+When DMAR is enabled for use, you will notice..
+
+PCI-DMA: Using DMAR IOMMU
+
+Fault reporting
+---------------
+
+DMAR:[DMA Write] Request device [00:02.0] fault addr 6df084000
+DMAR:[fault reason 05] PTE Write access is not set
+DMAR:[DMA Write] Request device [00:02.0] fault addr 6df084000
+DMAR:[fault reason 05] PTE Write access is not set
+
+TBD
+----
+
+- No Performance tuning / analysis yet.
+- sysfs needs useful data to be populated.
+ DMAR info, device scope, stats could be exposed to some extent.
+- Add support to Firmware Developer Kit to test ACPI tables for DMAR.
+- For compatibility testing, could use unity map domain for all devices, just
+ provide a 1-1 for all useful memory under a single domain for all devices.
+- API for paravirt ops for abstracting functionlity for VMM folks.
Index: linux-2.6.21-rc5/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.21-rc5.orig/Documentation/kernel-parameters.txt 2007-04-17 04:59:42.000000000 -0700
+++ linux-2.6.21-rc5/Documentation/kernel-parameters.txt 2007-04-17 05:41:56.000000000 -0700
@@ -710,6 +710,26 @@

inttest= [IA64]

+ intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
+ off
+ Disable intel iommu driver.
+ forcerw
+ Some drivers might incorrectly map DMA buffers as
+ write-only even when the device, requires read/write
+ mapping. This option works around the issue in IOMMU
+ driver by making all write-only map as read/write.
+ Default is off.
+ igfx_off [Default Off]
+ By default, gfx is mapped as normal device. If a gfx
+ device has a dedicated DMAR unit, the DMAR unit is
+ bypassed with this option. In this case, gfx device
+ will use physical address for DMA.
+ gfx_workaround [Default Off]
+ gfx devices tend to use physical address for DMA and
+ avoid using DMA api's. Setting this option permits
+ the IOMMU driver to set a unity map for all OS
+ visible memory. Hence the driver can continue to use
+ physical addresses for DMA.
io7= [HW] IO7 for Marvel based alpha systems
See comment before marvel_specify_io7 in
arch/alpha/kernel/core_marvel.c.

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