a68bd1267b
At the moment we allocate the entire TCE table, twice (hardware part and userspace translation cache). This normally works as we normally have contigous memory and the guest will map entire RAM for 64bit DMA. However if we have sparse RAM (one example is a memory device), then we will allocate TCEs which will never be used as the guest only maps actual memory for DMA. If it is a single level TCE table, there is nothing we can really do but if it a multilevel table, we can skip allocating TCEs we know we won't need. This adds ability to allocate only first level, saving memory. This changes iommu_table::free() to avoid allocating of an extra level; iommu_table::set() will do this when needed. This adds @alloc parameter to iommu_table::exchange() to tell the callback if it can allocate an extra level; the flag is set to "false" for the realmode KVM handlers of H_PUT_TCE hcalls and the callback returns H_TOO_HARD. This still requires the entire table to be counted in mm::locked_vm. To be conservative, this only does on-demand allocation when the usespace cache table is requested which is the case of VFIO. The example math for a system replicating a powernv setup with NVLink2 in a guest: 16GB RAM mapped at 0x0 128GB GPU RAM window (16GB of actual RAM) mapped at 0x244000000000 the table to cover that all with 64K pages takes: (((0x244000000000 + 0x2000000000) >> 16)*8)>>20 = 4556MB If we allocate only necessary TCE levels, we will only need: (((0x400000000 + 0x400000000) >> 16)*8)>>20 = 4MB (plus some for indirect levels). Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Reviewed-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
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 Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
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.