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The flush page DMA address is stored in a special register that is not
associated with the GPU's standard DMA range. For example, on Turing,
the GPU's MMU can handle 47-bit addresses, but the flush page address
register is limited to 40 bits.
At the point during device initialization when the flush page is
allocated, the DMA mask is still at its default of 32 bits. So even
though it's unlikely that the flush page could exist above a 40-bit
address, the dma_map_page() call could fail, e.g. if IOMMU is disabled
and the address is above 32 bits. The simplest way to achieve all
constraints is to allocate the page in the DMA32 zone. Since the flush
page is literally just a page, this is an acceptable limitation. The
alternative is to temporarily set the DMA mask to 40 (or 52 for Hopper
and later) bits, but that could have unforseen side effects.
In situations where the flush page is allocated above 32 bits and IOMMU
is disabled, you will get an error like this:
nouveau 0000:65:00.0: DMA addr 0x0000000107c56000+4096 overflow (mask ffffffff, bus limit 0).
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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 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.