From: Chris Brannon <cmb@prgmr.com>
To: alpine-user@lists.alpinelinux.org
Subject: Re: Syslinux & Xen & microcode updates
References: <alpine.DEB.2.21.99999.352.1910210236100.13135@trent.utfs.org>
Date: Mon, 21 Oct 2019 08:40:42 -0700
In-Reply-To: <alpine.DEB.2.21.99999.352.1910210236100.13135@trent.utfs.org>
	(Christian Kujau's message of "Mon, 21 Oct 2019 03:19:15 -0700 (PDT)")
Message-ID: <87r236t8cl.fsf@cmbmachine.messageid.invalid>
MIME-Version: 1.0
Content-Type: text/plain

Christian Kujau <lists@nerdbynature.de> writes:

> Hello,
>
> I'm having trouble applying CPU microcode updates to this system running a 
> Xen dom0. Lots of internet resources appear to recommend to add 
> "ucode=early_ucode.cpio" to the EFI xen.cfg configuration file and it will 
> magically work, but even though EFI support is now available[0], this 
> system of mine is using Syslinux to boot:

Hi,
ucode=scan should work reliably.  But you'll need to change your command
line in syslinux.  You have:

>  LABEL xen-vanilla
>    MENU LABEL Xen + Linux vanilla
>    COM32 mboot.c32
>    APPEND xen.gz dom0_mem=512M,max:1024M ucode=scan --- vmlinuz-vanilla \
>      root=[...] modules=ext4 --- initramfs-vanilla

Instead, would you try:

    APPEND xen.gz dom0_mem=512M,max:1024M ucode=scan --- vmlinuz-vanilla \
      root=[...] modules=ext4 --- intel-ucode.img --- initramfs-vanilla

That will pass in both the microcode file and initramfs.

> Also, combining microcode+intrd on the Syslinux command line[3] didn't 
> work either:
>
>   [...]
>   APPEND xen.gz dom0_mem=512M,max:1024M ucode=scan --- vmlinuz-vanilla 
>       root=[...] early_ucode.cpio,initramfs-vanilla
>
> Booting this failed with:
>
>    Loading xen.gz.... ok
>    Loading vmlinuz-vanilla... ok
>    Loading early_ucode.cpio,initramfs-vanilla... failed!
>    No files found!

Yes, I'm pretty sure this was a syntax issue with syslinux.  But the
syntax I gave earlier should work.

FWIW there is a subtle difference in how microcode is handled on EFI and
non-EFI Xen.  For non-EFI Xen, the ucode= parameter is either a
zero-based index into the list of loaded modules, the value "scan" to
scan the list, or -1 to use the last module in the list.  See here:
https://xenbits.xenproject.org/docs/4.12-testing/misc/xen-command-line.html#ucode-x86

On the other hand, EFI Xen takes ucode=<filename> as a parameter in a
configuration file.  I don't have any experience with EFI Xen.

Does that help?

-- Chris