Re: [Xen-devel] [PATCH] x86/microcode: Support builtin CPU microcode

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.12.2019 22:49, Eslam Elnikety wrote:
> On 09.12.19 16:19, Andrew Cooper wrote:
>> On 09/12/2019 08:41, Eslam Elnikety wrote:
>>> --- /dev/null
>>> +++ b/xen/arch/x86/microcode/Makefile
>>> @@ -0,0 +1,40 @@
>>> +# Copyright (C) 2019 Amazon.com, Inc. or its affiliates.
>>> +# Author: Eslam Elnikety <elnikety@xxxxxxxxxx>
>>> +#
>>> +# This program is free software; you can redistribute it and/or modify
>>> +# it under the terms of the GNU General Public License as published by
>>> +# the Free Software Foundation; either version 2 of the License, or
>>> +# (at your option) any later version.
>>> +#
>>> +# This program is distributed in the hope that it will be useful,
>>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> +# GNU General Public License for more details.
>>> +
>>> +obj-y += builtin_ucode.o
>>> +
>>> +# Directory holding the microcode updates.
>>> +UCODE_DIR=$(patsubst "%",%,$(CONFIG_BUILTIN_UCODE_DIR))
>>> +amd-blobs := $(wildcard $(UCODE_DIR)/amd-ucode/*)
>>> +intel-blobs := $(wildcard $(UCODE_DIR)/intel-ucode/*)
>>
>> This is a little dangerous.  I can see why you want to do it like this,
>> and I can't provide any obvious suggestions, but if this glob picks up
>> anything which isn't a microcode file, it will break the logic to search
>> for the right blob.
>>
> 
> We can limit the amd-blobs and intel-blob to binaries following the 
> naming convention AuthenticAMD.bin and GenuineIntel.bin for amd and 
> intel, respectively. Yet, this would be imposing an unnecessary 
> restriction on administrators who may want to be innovative with naming 
> (or want to use the naming microcode_amd_*.bin or FF-MM-SS instead).
> 
> Alternatively, we can introduce CONFIG_BUILTIN_UCODE_INTEL and 
> CONFIG_BUILTIN_UCODE_AMD. Both default to empty strings. Then, an 
> administrator can specify exactly the microcodes to include relative to 
> the CONFIG_BUILTIN_UCODE_DIR. For example:
> CONFIG_BUILTIN_UCODE_INTEL="intel-ucode/06-3a-09"
> CONFIG_BUILTIN_UCODE_AMD="amd-ucode/microcode_amd_fam15h.bin"

This would make the feature even less generic - I already meant to
ask whether building ucode into binaries is really a useful thing
when we already have more flexible ways. I could see this being
useful if there was no other way to make ucode available at boot
time.

Jan

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