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docs, amd_ucode: add AMD container file format notes
This patch introduces documentation notes about AMD container file formats and where to obtain latest container files from. Also, We provide a how-to for updating patch level by concatenating container files along with initrd images. Misc notes about how Xen handles two containers of same kind (if/when) they are concatenated together are also included. Signed-off-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>
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Aravind Gopalakrishnan authored and Jan Beulich committed
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AMD Microcode Container File format
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-------------------------------------------------
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Author:
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Aravind [dot] Gopalakrishnan [at] amd [dot] com
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Initial version:
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July 2014
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Updated:
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October 2014
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-------------------------------------------------
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Intro to AMD Container Files:
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-----------------------------
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* AMD provides microcode patch support for processors belonging to AMD
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processor families 10h, 11h, 12h, 14h, and 15h.
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* There is one single file (container file) containing all microcode patches
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for AMD families 10h - 14h processors. [microcode_amd.bin]
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* For AMD family 15h processors there is a separate container file. [microcode_amd_fam15h.bin]
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* Microcode patches are not incremental, therefore you only need to make
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sure you have the latest container file for your AMD processor family.
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* One can find the latest AMD microcode containers from [1], [2]
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Mutual Exclusivity Rule of AMD containers:
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* The patches for families 10h - 14h are guaranteed to be only on
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microcode_amd.bin
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* Similarly, patches for family 15h will only be on microcode_amd_fam15h.bin
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* This is because, the processes and scripts used to create container files
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ensure that there is no mix-up
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Microcode patch header structure:
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---------------------------------
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struct __packed microcode_header_amd {
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uint32_t data_code;
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uint32_t patch_id;
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uint8_t mc_patch_data_id[2];
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uint8_t mc_patch_data_len;
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uint8_t init_flag;
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uint32_t mc_patch_data_checksum;
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uint32_t nb_dev_id;
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uint32_t sb_dev_id;
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uint16_t processor_rev_id;
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uint8_t nb_rev_id;
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uint8_t sb_rev_id;
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uint8_t bios_api_rev;
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uint8_t reserved1[3];
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uint32_t match_reg[8];
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}
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More details about microcode patch header are typically not exposed to public.
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Apply microcode updates using initrd:
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-------------------------------------
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Initrd images can be modified to contain AMD microcode containers in cpio
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format at the start of the image.
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Following example shows how to generate a combined initrd
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Note: initrd-<val> could be different on your machine. Substitute accordingly
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Example System base: Ubuntu 13.04 with 3.8.0-30-generic kernel
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1. mkdir initrd-for-xen-with_append
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2. cd initrd-for-xen-with_append
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3. mkdir -p kernel/x86/microcode
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4. cp /lib/firmware/amd-ucode/microcode_amd.bin .
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5. cp /lib/firmware/amd-ucode/microcode_amd_fam15h.bin .
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6. cat microcode_amd.bin microcode_amd_fam15h.bin > microcode_concatenated.bin
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7. mv microcode_concatenated.bin kernel/x86/microcode/AuthenticAMD.bin
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8. rm microcode_amd.bin microcode_amd_fam15h.bin
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9. find . | cpio -o -H newc > ucode.cpio
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10. cp /boot/initrd.img-3.8.0-30-generic .
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11. cat ucode.cpio initrd.img-3.8.0-30-generic > initrd_for_xen_with_ucode
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12. cp initrd_for_xen_with_ucode /boot/
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13. On grub.cfg, provide the above initrd name as module.
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14. Use 'ucode=scan' option as Xen boot parameter.
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Misc Notes:
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-----------
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It is not recommended to concatenate two(or more) container files of
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the same kind. (two microcode_amd_fam15h.bin for example)
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This is because:
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There is no check in Xen currently to verify this.
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Now, given a situation where
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1. An earlier container has a patch that 'fits' the processor you are
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currently on,
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2. There is a subsequent container that *also* has a patch that 'fits',
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3. The second patch happens to be an update over the patch found on the
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first container file.
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In such a case, only the patch from the first container is applied.
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This is because Xen assumes that the the containers (if concatenated
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together) are different kinds AND the 'Mutual Exclusivity' rule is
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always true.
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In cases where users are not sure about provenance of containers
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they should obtain a "good" set by downloading them from source links
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[1], [2] since it's not guaranteed that the latest patch will be applied.
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Reference(s):
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-------------
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[1] http://www.amd64.org/microcode.html
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[2] https://git.kernel.org/cgit/linux/kernel/git/firmware/linux-firmware.git/tree/amd-ucode
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[3] http://lxr.free-electrons.com/source/Documentation/x86/early-microcode.txt
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