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4440337af4
Remove superfluous RSB filling after a VMEXIT when the CPU already has flushed the RSB after a VMEXIT when AutoIBRS is enabled. The initial implementation for adding RETPOLINES added an ALTERNATIVES implementation for filling the RSB after a VMEXIT in commit117cc7a908("x86/retpoline: Fill return stack buffer on vmexit"). Later, X86_FEATURE_RSB_VMEXIT was added in commit9756bba284("x86/speculation: Fill RSB on vmexit for IBRS") to handle stuffing the RSB if RETPOLINE=y *or* KERNEL_IBRS=y, i.e. to also stuff the RSB if the kernel is configured to do IBRS mitigations on entry/exit. The AutoIBRS (on AMD) feature implementation added in commite7862eda30("x86/cpu: Support AMD Automatic IBRS") used the already-implemented logic for EIBRS in spectre_v2_determine_rsb_fill_type_on_vmexit() -- but did not update the code at VMEXIT to act on the mode selected in that function -- resulting in VMEXITs continuing to clear the RSB when RETPOLINES are enabled, despite the presence of AutoIBRS. Signed-off-by: Amit Shah <amit.shah@amd.com> Link: https://lore.kernel.org/r/20240807123531.69677-1-amit@kernel.org [sean: massage changeloge, drop comment about AMD not needing RSB_VMEXIT_LITE] Signed-off-by: Sean Christopherson <seanjc@google.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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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.