Subject: Re: Can't boot as Xen dom0 due to commit fe055896
To: Borislav Petkov <bp@suse.de>
References: <73a4d64b-b139-6579-a560-92311641d6c7@suse.com>
 <20161215164635.thm7ruio2ddnxszw@pd.tnic>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        xen-devel <xen-devel@lists.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
From: Juergen Gross <jgross@suse.com>
Message-ID: <7d5500be-7bf6-4b6e-063d-6f5a8d031115@suse.com>
Date: Thu, 15 Dec 2016 18:06:29 +0100
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On 15/12/16 17:46, Borislav Petkov wrote:
> On Thu, Dec 15, 2016 at 05:12:04PM +0100, Juergen Gross wrote:
>> with today's kernel the system isn't coming up when booted as Xen dom0:
> 
> Remind me again pls, is dom0 even supposed to load microcode? Isn't the
> hypervisor supposed to apply microcode?
> 
>> Looking into the state of cpu 1 I find the following backtrace (created
>> manually by looking up addresses from a stack dump retrieved from the
>> hypervisor):
>>
>> find_cpio_data()
>> find_microcode_in_initrd()
>> __load_ucode_intel()
>> load_ucode_intel_ap()
>> cpu_init()
>> cpu_bringup()
>> cpu_bringup_and_idle()
>>
>> It seems as if load_ucode_intel_ap() is looping. You introduced a
>> possibly endless loop in it with commit fe055896.
> 
> Are you sure you mean:
> 
>   fe055896c040 ("x86/microcode: Merge the early microcode loader")
> 
> because that commit is a year old.

OMG. Sorry, somehow I managed to read the date of that patch wrong.

> So from looking at the *current* code:
> 
> 	if (apply_microcode_early(&uci, true)) {
> 
> fails probably because MSR_IA32_UCODE_REV doesn't get read properly due
> to virtualized MSRs, bla, yadda yadda...

I'll check.

BTW: Adding a retry count doesn't help. Just tried.

> But before we debug this further, I'd like to make sure I'm debugging
> the proper thing and not some situation again where xen wasn't even
> supposed to run the microcode loader but it does it anyway...

I guess this might be the case.


Juergen