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Balbir Singh ee2a06bbbb x86/mm/init: Handle the special case of device private pages in add_pages(), to not increase max_pfn and trigger dma_addressing_limited() bounce buffers bounce buffers 
commit 7170130e4c upstream.

As Bert Karwatzki reported, the following recent commit causes a
performance regression on AMD iGPU and dGPU systems:

  7ffb791423 ("x86/kaslr: Reduce KASLR entropy on most x86 systems")

It exposed a bug with nokaslr and zone device interaction.

The root cause of the bug is that, the GPU driver registers a zone
device private memory region. When KASLR is disabled or the above commit
is applied, the direct_map_physmem_end is set to much higher than 10 TiB
typically to the 64TiB address. When zone device private memory is added
to the system via add_pages(), it bumps up the max_pfn to the same
value. This causes dma_addressing_limited() to return true, since the
device cannot address memory all the way up to max_pfn.

This caused a regression for games played on the iGPU, as it resulted in
the DMA32 zone being used for GPU allocations.

Fix this by not bumping up max_pfn on x86 systems, when pgmap is passed
into add_pages(). The presence of pgmap is used to determine if device
private memory is being added via add_pages().

More details:

devm_request_mem_region() and request_free_mem_region() request for
device private memory. iomem_resource is passed as the base resource
with start and end parameters. iomem_resource's end depends on several
factors, including the platform and virtualization. On x86 for example
on bare metal, this value is set to boot_cpu_data.x86_phys_bits.
boot_cpu_data.x86_phys_bits can change depending on support for MKTME.
By default it is set to the same as log2(direct_map_physmem_end) which
is 46 to 52 bits depending on the number of levels in the page table.
The allocation routines used iomem_resource's end and
direct_map_physmem_end to figure out where to allocate the region.

[ arch/powerpc is also impacted by this problem, but this patch does not fix
  the issue for PowerPC. ]

Testing:

 1. Tested on a virtual machine with test_hmm for zone device inseration

 2. A previous version of this patch was tested by Bert, please see:
    https://lore.kernel.org/lkml/d87680bab997fdc9fb4e638983132af235d9a03a.camel@web.de/

[ mingo: Clarified the comments and the changelog. ]

Reported-by: Bert Karwatzki <spasswolf@web.de>
Tested-by: Bert Karwatzki <spasswolf@web.de>
Fixes: 7ffb791423 ("x86/kaslr: Reduce KASLR entropy on most x86 systems")
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Link: https://lore.kernel.org/r/20250401000752.249348-1-balbirs@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-05-29 11:03:26 +02:00
arch x86/mm/init: Handle the special case of device private pages in add_pages(), to not increase max_pfn and trigger dma_addressing_limited() bounce buffers bounce buffers 2025-05-29 11:03:26 +02:00
block block: only update request sector if needed 2025-05-29 11:03:12 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: algif_hash - fix double free in hash_accept 2025-05-29 11:03:18 +02:00
Documentation serial: mctrl_gpio: split disable_ms into sync and no_sync APIs 2025-05-29 11:02:45 +02:00
drivers i3c: master: svc: Fix implicit fallthrough in svc_i3c_master_ibi_work() 2025-05-29 11:03:26 +02:00
fs ksmbd: fix stream write failure 2025-05-29 11:03:24 +02:00
include err.h: move IOMEM_ERR_PTR() to err.h 2025-05-29 11:03:25 +02:00
init rust: clean Rust 1.88.0's unnecessary_transmutes lint 2025-05-18 08:24:51 +02:00
io_uring io_uring: fix overflow resched cqe reordering 2025-05-29 11:03:17 +02:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel bpf: abort verification if env->cur_state->loop_entry != NULL 2025-05-29 11:03:25 +02:00
lib crypto: lzo - Fix compression buffer overrun 2025-05-29 11:02:25 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: vmalloc: only zero-init on vrealloc shrink 2025-05-29 11:03:23 +02:00
net net: dsa: microchip: linearize skb for tail-tagging switches 2025-05-29 11:03:20 +02:00
rust rust: clean Rust 1.88.0's clippy::uninlined_format_args lint 2025-05-18 08:24:57 +02:00
samples samples/bpf: Fix compilation failure for samples/bpf on LoongArch Fedora 2025-05-29 11:02:01 +02:00
scripts kbuild: Properly disable -Wunterminated-string-initialization for clang 2025-05-29 11:03:25 +02:00
security smack: Revert "smackfs: Added check catlen" 2025-05-29 11:02:48 +02:00
sound ALSA: hda/realtek: Add quirk for Lenovo Yoga Pro 7 14ASP10 2025-05-29 11:03:20 +02:00
tools tools: ynl-gen: validate 0 len strings from kernel 2025-05-29 11:03:12 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Add member to struct kvm_gfn_range to indicate private/shared 2025-05-22 14:29:36 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-18 08:24:51 +02:00
.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 rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.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: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
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 MAINTAINERS: Update Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile kbuild: Properly disable -Wunterminated-string-initialization for clang 2025-05-29 11:03:25 +02:00
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.