linux-kernel - Re: [PATCH] x86/microcode: Allow early loading without initrd

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Date:	Sun, 26 Apr 2015 18:16:09 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Alexander Hirsch <1zeeky@...il.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/microcode: Allow early loading without initrd

On Sun, Apr 26, 2015 at 05:03:14PM +0200, Alexander Hirsch wrote:
> Microcode can be baked into the kernel image via CONFIG_EXTRA_FIRMWARE
> and the early loader supports that, but still depended on
> BLK_DEV_INITRD.
> This dependency is removed.

Yeah, it is removed but it adds a bunch of ugly ifdeffery which makes
the code even more unreadable than it is :-\

> Signed-off-by: Alexander Hirsch <1zeeky@...il.com>
> ---
>
> This patch depends on the "Parse built-in microcode early" patch by
> Borislav Petkov (https://lkml.org/lkml/2015/4/1/331).

In the future, please CC me on microcode loader patches.

> I only tested this on two Intel machines (an i3 M330 and an i5-4690).
> There is no change in amd_early.c because it compiles fine - only
> intel_early.c complained without BLK_DEV_INITRD.

Right, so I see what you're trying to achieve and I'd guess your
reasoning is that BLK_DEV_INITRD is not really needed if you build your
microcode into the kernel. And that's ok but I'm not persuaded yet:

* why do you even bother - BLK_DEV_INITRD gets enabled on all distro
kernels and almost everything running Linux so why bother? Or do you
have a special use case which doesn't want BLK_DEV_INITRD. I'd be
interested to hear about it.

* the early loader was done with initrd in mind and it was/still is its
main source for microcode blobs early in the boot. So if we want to
make it not-mandatory, then the driver needs to be reorganized so that
builtin blobs and initrd blobs loading paths are cleanly untangled. The
ifdeffery thing might work now but is certainly not future-proof so it
would need to be designed in a cleaner way.

Perhaps something like a microcode cache of patches the AMD loader has,
all decoupled from the loading paths or so... I don't have a good idea
right now. I'll have to think about it.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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