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Reading DR[0-3]_ADDR_MASK MSRs takes about 250 cycles which is going to be noticeable with the AMD KVM SEV-ES DebugSwap feature enabled. KVM is going to store host's DR[0-3] and DR[0-3]_ADDR_MASK before switching to a guest; the hardware is going to swap these on VMRUN and VMEXIT. Store MSR values passed to set_dr_addr_mask() in percpu variables (when changed) and return them via new amd_get_dr_addr_mask(). The gain here is about 10x. As set_dr_addr_mask() uses the array too, change the @dr type to unsigned to avoid checking for <0. And give it the amd_ prefix to match the new helper as the whole DR_ADDR_MASK feature is AMD-specific anyway. While at it, replace deprecated boot_cpu_has() with cpu_feature_enabled() in set_dr_addr_mask(). Signed-off-by: Alexey Kardashevskiy <aik@amd.com> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Link: https://lore.kernel.org/r/20230120031047.628097-2-aik@amd.com
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.