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Joao Martins 7a7bba1624 iommufd/iova_bitmap: Dynamic pinning on iova_bitmap_set() 
Today zerocopy iova bitmaps use a static iteration scheme where it walks
the bitmap data in a max iteration size of 2M of bitmap of data at a time.
That translates to a fixed window of IOVA space that can span up to 64G
(e.g.  base pages, x86). Here 'window' refers to the IOVA space represented
by the bitmap data it is iterating. This static scheme is the ideal one
where the reported page-size is the same as the one behind the dirty
tracker.

However, problems start to appear when the dirty tracker may
dirty in many PTE sizes beyond or unaligned at the boundaries of the
iteration window. Such is the case for the IOMMU and
commit 2780025e01 ("iommufd/iova_bitmap: Handle recording beyond the mapped pages")
tried to fix the problem by handling the PTEs that get dirty which
surprass the end of the iteration. But the fix was incomplete and it
didn't handle all the data structure issues namely:

1) when there's nothing to dirty but the end of the iteration IOVA range is
a IOMMU hugepage PTE that crosses iterations, when it goes to the next
iteration it finds the other end of the said hugepage but don't account that
it had checked for that IOPTE already. iommu driver then walk the IOVA
space as if it is a new page without accounting that it is past the start
of a bigger page which ends up setting (future) dirty bits slightly
offset-ed. Note that the partial ranges here are self induced
due as a result of the fixed 'window' scheme being unaligned to this
hugepage IOPTE.

2) on the same line of thinking between pinning pages of different
iterations it could allow DMA to mark PTEs as dirty on the second part of
this previously mentioned partial hugepage. This leads to marking part of
the hugepage as dirty but still clearing IOPTE leading to missed dirty
data.

So to fix these problems more fundamentally and avoid future ones: instead
of iterating the whole bitmap in fixed chunks, instead only pin the bitmap
pages when it has dirty bits to set. The logic is simple in
iova_bitmap_set(): check where the current iova range to be marked as dirty
is pinned and pin the bitmap pages where to-be-recorded @iova starts if
it's not. If it's partially mapped out of the whole set, continue pinning
it and set bits until the whole dirty-size is covered. The latter is more
relevant with AMD iommu pgtable v1 format where you can have up
64G/128G/256G page sizes and thus you can set 64G at a time. Code also gets
simpler and easier to follow.

Fixing this without changing this iteration scheme means changing iommu
drivers to ignore any partial pages and not clear dirty bits, which is a
bit hacky. Though getting to walk only part of a IOMMU hugepage is a
self-induced due to this iteration scheme as it doesn't (and can't) align the
iteration boundary to the huge IOPTE at the end. Thus it can't know what
the hugepage size the iteration should align to until it walks the begin/end.

Dynamically pinning adds some comparisons inside iova_bitmap_set() to check
if something needs to be pinned if the IOVA range is out of range. Though
it has the benefit that non-dirty IOVA ranges only walk page tables without
needing to pin any bitmap pages. This dynamic scheme should be better for IOMMUs
where upper layers don't need or know what PTE sizes IOVAs map into (and there
could be more than one PTE size[*]) until they walk the IOMMU page tables.

A follow-up change will remove the iteration logic.

[*] Specially on AMD v1 iommu pgtable format where most powers of two are
supported as page-size.

Link: https://lore.kernel.org/linux-iommu/6b90f949-48da-4cb3-ad9a-ed54f1351a9a@oracle.com/
Fixes: 2780025e01 ("iommufd/iova_bitmap: Handle recording beyond the mapped pages")
Link: https://lore.kernel.org/r/20240627110105.62325-11-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Matt Ochs <mochs@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
2024-06-28 13:12:23 -03:00
arch - fix lseek in o32 compat mode 2024-06-23 07:20:02 -07:00
block block: unmap and free user mapped integrity via submitter 2024-06-12 11:00:50 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto This push fixes a bug in the new ecc P521 code as well as a buggy 2024-05-20 08:47:54 -07:00
Documentation The core gains placeholders for recently added functions when CONFIG_I2C 2024-06-23 11:06:01 -04:00
drivers iommufd/iova_bitmap: Dynamic pinning on iova_bitmap_set() 2024-06-28 13:12:23 -03:00
fs Five smb3 client fixes 2024-06-23 11:01:57 -04:00
include The core gains placeholders for recently added functions when CONFIG_I2C 2024-06-23 11:06:01 -04:00
init gcc: disable '-Warray-bounds' for gcc-9 2024-06-15 10:43:04 -07:00
io_uring io_uring/rsrc: fix incorrect assignment of iter->nr_segs in io_import_fixed 2024-06-20 06:51:56 -06:00
ipc Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
kernel Including fixes from wireless, bpf and netfilter. 2024-06-20 10:49:50 -07:00
lib bcachefs fixes for 6.10-rc5 2024-06-22 09:02:39 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm memblock: fix fragility in checks for unset node ID 2024-06-23 10:32:24 -04:00
net nfsd-6.10 fixes: 2024-06-22 13:55:56 -07:00
rust rust: avoid unused import warning in rusttest 2024-06-11 23:33:28 +02:00
samples tracing/treewide: Remove second parameter of __assign_str() 2024-05-22 20:14:47 -04:00
scripts Kbuild fixes for v6.10 (second) 2024-06-08 10:12:33 -07:00
security lsm/stable-6.10 PR 20240617 2024-06-17 18:35:12 -07:00
sound ALSA: hda: Use imply for suggesting CONFIG_SERIAL_MULTI_INSTANTIATE 2024-06-21 12:04:19 +02:00
tools iommufd/selftest: Fix tests to use MOCK_PAGE_SIZE based buffer sizes 2024-06-28 13:12:22 -03:00
usr kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
virt KVM fixes for 6.10 2024-06-21 08:03:55 -04:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap bpf-for-netdev 2024-06-14 17:57:10 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer 2024-03-27 13:41:02 -05:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS ARM: 2024-06-22 07:41:57 -07:00
Makefile Linux 6.10-rc5 2024-06-23 17:08:54 -04:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

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.