69f5f98300
The idea was to not scan the microcode blob on each AP (Application Processor) during boot and thus save us some milliseconds. However, on architectures where the microcode engine is shared between threads, this doesn't work. Here's why: The microcode on CPU0, i.e., the first thread, gets updated. The second thread, i.e., CPU1, i.e., the first AP walks into load_ucode_amd_ap(), sees that there's no container cached and goes and scans for the proper blob. It finds it and as a last step of apply_microcode_early_amd(), it tries to apply the patch but that core has already the updated microcode revision which it has received through CPU0's update. So it returns false and we do desc->size = -1 to prevent other APs from scanning. However, the next AP, CPU2, has a different microcode engine which hasn't been updated yet. The desc->size == -1 test prevents it from scanning the blob anew and we fail to update it. The fix is much more straight-forward than it looks: the BSP (BootStrapping Processor), i.e., CPU0, caches the microcode patch in amd_ucode_patch. We use that on the AP and try to apply it. In the 99.9999% of cases where we have homogeneous cores - *not* mixed-steppings - the application will be successful and we're good to go. In the remaining small set of systems, we will simply rescan the blob and find (or not, if none present) the proper patch and apply it then. Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20170120202955.4091-16-bp@alien8.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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| drivers | ||
| firmware | ||
| fs | ||
| include | ||
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| ipc | ||
| kernel | ||
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| samples | ||
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| README | ||
README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.