path: root/Documentation/x86
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authorLinus Torvalds <torvalds@linux-foundation.org>2013-02-22 19:22:52 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-22 19:22:52 -0800
commitc47f39e3b75e1138823984ad5079547c7a41b726 (patch)
tree0f4d5c304e049521f2bcdc35272679f1cac75489 /Documentation/x86
parent0cc9129d75ef8993702d97ab0e49542c15ac6ab9 (diff)
parentda76f64e7eb28b718501d15c1b79af560b7ca4ea (diff)
Merge branch 'x86/microcode' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 microcode loading update from Peter Anvin: "This patchset lets us update the CPU microcode very, very early in initialization if the BIOS fails to do so (never happens, right?) This is handy for dealing with things like the Atom erratum where we have to run without PSE because microcode loading happens too late. As I mentioned in the x86/mm push request it depends on that infrastructure but it is otherwise a standalone feature." * 'x86/microcode' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/Kconfig: Make early microcode loading a configuration feature x86/mm/init.c: Copy ucode from initrd image to kernel memory x86/head64.c: Early update ucode in 64-bit x86/head_32.S: Early update ucode in 32-bit x86/microcode_intel_early.c: Early update ucode on Intel's CPU x86/tlbflush.h: Define __native_flush_tlb_global_irq_disabled() x86/microcode_intel_lib.c: Early update ucode on Intel's CPU x86/microcode_core_early.c: Define interfaces for early loading ucode x86/common.c: load ucode in 64 bit or show loading ucode info in 32 bit on AP x86/common.c: Make have_cpuid_p() a global function x86/microcode_intel.h: Define functions and macros for early loading ucode x86, doc: Documentation for early microcode loading
Diffstat (limited to 'Documentation/x86')
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diff --git a/Documentation/x86/early-microcode.txt b/Documentation/x86/early-microcode.txt
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+Early load microcode
+By Fenghua Yu <fenghua.yu@intel.com>
+Kernel can update microcode in early phase of boot time. Loading microcode early
+can fix CPU issues before they are observed during kernel boot time.
+Microcode is stored in an initrd file. The microcode is read from the initrd
+file and loaded to CPUs during boot time.
+The format of the combined initrd image is microcode in cpio format followed by
+the initrd image (maybe compressed). Kernel parses the combined initrd image
+during boot time. The microcode file in cpio name space is:
+During BSP boot (before SMP starts), if the kernel finds the microcode file in
+the initrd file, it parses the microcode and saves matching microcode in memory.
+If matching microcode is found, it will be uploaded in BSP and later on in all
+The cached microcode patch is applied when CPUs resume from a sleep state.
+There are two legacy user space interfaces to load microcode, either through
+/dev/cpu/microcode or through /sys/devices/system/cpu/microcode/reload file
+in sysfs.
+In addition to these two legacy methods, the early loading method described
+here is the third method with which microcode can be uploaded to a system's
+The following example script shows how to generate a new combined initrd file in
+/boot/initrd-3.5.0.ucode.img with original microcode microcode.bin and
+original initrd image /boot/initrd-3.5.0.img.
+mkdir initrd
+cd initrd
+mkdir kernel
+mkdir kernel/x86
+mkdir kernel/x86/microcode
+cp ../microcode.bin kernel/x86/microcode/GenuineIntel.bin
+find .|cpio -oc >../ucode.cpio
+cd ..
+cat ucode.cpio /boot/initrd-3.5.0.img >/boot/initrd-3.5.0.ucode.img

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