linux-kernel - Re: Can't boot as Xen dom0 due to commit fe055896

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Date:   Thu, 15 Dec 2016 14:08:50 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Juergen Gross <jgross@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>
Subject: Re: Can't boot as Xen dom0 due to commit fe055896

On 12/15/2016 12:36 PM, Borislav Petkov wrote:
> On Thu, Dec 15, 2016 at 12:27:49PM -0500, Boris Ostrovsky wrote:
>> It will probably fix it but I don't think we want this: it's a
>> build-time solution. Most kernels have XEN on even though they are
>> booted bare-metal.
> Lemme tell you want I want: a way to detect I'm running on xen. Does
> CPUID(4) work really early, at load_ucode_bsp() time?
>
> IOW, can I use some of the functionality hypervisor_cpuid_base() uses to
> detect xen and stop loading any further?

I think we need at least

diff --git a/arch/x86/kernel/cpu/microcode/amd.c
b/arch/x86/kernel/cpu/microcode/amd.c
index 6f353bd..383b635 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -427,7 +427,7 @@ int __init save_microcode_in_initrd_amd(unsigned int
fam)
 {
        enum ucode_state ret;
        int retval = 0;
-       u16 eq_id;
+       u16 eq_id = 0;
 
        if (!cont.data) {
                if (IS_ENABLED(CONFIG_X86_32) && (cont.size != -1)) {



This fixes my PV boot problem. I am still failing to boot HVM, will need
to look at this some more.

-boris