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commit5f465c148cupstream. Initialize DR6 by writing its architectural reset value to avoid incorrectly zeroing DR6 to clear DR6.BLD at boot time, which leads to a false bus lock detected warning. The Intel SDM says: 1) Certain debug exceptions may clear bits 0-3 of DR6. 2) BLD induced #DB clears DR6.BLD and any other debug exception doesn't modify DR6.BLD. 3) RTM induced #DB clears DR6.RTM and any other debug exception sets DR6.RTM. To avoid confusion in identifying debug exceptions, debug handlers should set DR6.BLD and DR6.RTM, and clear other DR6 bits before returning. The DR6 architectural reset value 0xFFFF0FF0, already defined as macro DR6_RESERVED, satisfies these requirements, so just use it to reinitialize DR6 whenever needed. Since clear_all_debug_regs() no longer zeros all debug registers, rename it to initialize_debug_regs() to better reflect its current behavior. Since debug_read_clear_dr6() no longer clears DR6, rename it to debug_read_reset_dr6() to better reflect its current behavior. Fixes:ebb1064e7c("x86/traps: Handle #DB for bus lock") Reported-by: Sohil Mehta <sohil.mehta@intel.com> Suggested-by: H. Peter Anvin (Intel) <hpa@zytor.com> Signed-off-by: Xin Li (Intel) <xin@zytor.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com> Reviewed-by: Sohil Mehta <sohil.mehta@intel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Sohil Mehta <sohil.mehta@intel.com> Link: https://lore.kernel.org/lkml/06e68373-a92b-472e-8fd9-ba548119770c@intel.com/ Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20250620231504.2676902-2-xin%40zytor.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 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.