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This is used by x86 CPUs and can be used in AMD/VT-d x86 IOMMUs. When a
x86 IOMMU is running SVA the MM will be using this format.
This implementation follows the AMD v2 io-pgtable version.
There is nothing remarkable here, the format can have 4 or 5 levels and
limited support for different page sizes. No contiguous pages support.
x86 uses a sign extension mechanism where the top bits of the VA must
match the sign bit. The core code supports this through
PT_FEAT_SIGN_EXTEND which creates and upper and lower VA range. All the
new operations will work correctly in both spaces, however currently there
is no way to report the upper space to other layers. Future patches can
improve that.
In principle this can support 3 page tables levels matching the 32 bit PAE
table format, but no iommu driver needs this. The focus is on the modern
64 bit 4 and 5 level formats.
Comparing the performance of several operations to the existing version:
iommu_map()
pgsz ,avg new,old ns, min new,old ns , min % (+ve is better)
2^12, 71,61 , 66,58 , -13.13
2^21, 66,60 , 61,55 , -10.10
2^30, 59,56 , 56,54 , -3.03
256*2^12, 392,1360 , 345,1289 , 73.73
256*2^21, 383,1159 , 335,1145 , 70.70
256*2^30, 378,965 , 331,892 , 62.62
iommu_unmap()
pgsz ,avg new,old ns, min new,old ns , min % (+ve is better)
2^12, 77,71 , 73,68 , -7.07
2^21, 76,70 , 70,66 , -6.06
2^30, 69,66 , 66,63 , -4.04
256*2^12, 225,899 , 210,870 , 75.75
256*2^21, 262,722 , 248,710 , 65.65
256*2^30, 251,643 , 244,634 , 61.61
The small -ve values in the iommu_unmap() are due to the core code calling
iommu_pgsize() before invoking the domain op. This is unncessary with this
implementation. Future work optimizes this and gets to 2%, 4%, 3%.
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Tested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Tested-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.