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[ Upstream commit 7ffb791423c7c518269a9aad35039ef824a40adb ] When CONFIG_PCI_P2PDMA=y (which is basically enabled on all large x86 distros), it maps the PFN's via a ZONE_DEVICE mapping using devm_memremap_pages(). The mapped virtual address range corresponds to the pci_resource_start() of the BAR address and size corresponding to the BAR length. When KASLR is enabled, the direct map range of the kernel is reduced to the size of physical memory plus additional padding. If the BAR address is beyond this limit, PCI peer to peer DMA mappings fail. Fix this by not shrinking the size of the direct map when CONFIG_PCI_P2PDMA=y. This reduces the total available entropy, but it's better than the current work around of having to disable KASLR completely. [ mingo: Clarified the changelog to point out the broad impact ... ] Signed-off-by: Balbir Singh <balbirs@nvidia.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Kees Cook <kees@kernel.org> Acked-by: Bjorn Helgaas <bhelgaas@google.com> # drivers/pci/Kconfig Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Link: https://lore.kernel.org/lkml/20250206023201.1481957-1-balbirs@nvidia.com/ Link: https://lore.kernel.org/r/20250206234234.1912585-1-balbirs@nvidia.com -- arch/x86/mm/kaslr.c | 10 ++++++++-- drivers/pci/Kconfig | 6 ++++++ 2 files changed, 14 insertions(+), 2 deletions(-) Signed-off-by: Sasha Levin <sashal@kernel.org>
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.
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.