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

[Eslam Elnikety <elnikety@xxxxxxxxxx>]

On 10.12.19 10:21, Jan Beulich wrote:
> 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
I do not follow the point about being less generic. (I hope my example 
did not give the false impression that CONFIG_BUILTIN_UCODE_{AMD,INTEL} 
allow for only a single microcode blob for a single signature).
> 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.
It is useful in addition to the existing ways to do early microcode 
updates. First, when operating many hosts, using boot modules (either a 
distinct microcode module or within an initrd) becomes involved. For 
instance, tools to update boot entries (e.g., 
https://linux.die.net/man/8/grubby) do not support adding arbitrary 
(microcode) modules.
Second, there is often need to couple a Xen build with a minimum 
microcode patch level. Having the microcode built within the Xen image 
itself is a streamlined, natural way of achieving that.
Thanks,
Eslam

> Jan

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