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

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Message-ID: <399c758a-a94b-8aa1-efbb-79a0161b8020@oracle.com>
Date:   Thu, 15 Dec 2016 14:36:46 -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 02:23 PM, Borislav Petkov wrote:
> On Thu, Dec 15, 2016 at 02:08:50PM -0500, Boris Ostrovsky wrote:
>> This fixes my PV boot problem. I am still failing to boot HVM, will
>> need to look at this some more.
> No, no more stabbing in the dark and no more brown paper bags.

This fixes a bug that has nothing to do with Xen.

We are calling find_proper_container(..., &eq_id) and determine result
based on eq_id not being zero. If find_proper_container() doesn't find
anything it will not modify eq_id and so you get back whatever you
passed in.

What the patch that I sent does is no different from how
apply_microcode_early_amd() makes the call to find_proper_container.

The fact that  I am having problems with HVM may or may not have
anything to do with microcode. I don't know yet but it's separate from
save_microcode_in_initrd_amd() patch. I am pretty sure about that
because unlike PV it is failing in early boot code.

-boris

>
> Please check whether CPUID(4) works that early in any xen guest and
> let's add that check to a function which does something like:
>
> bool loader_disabled(void)
> {
> 	if (running_on_a_xen_guest)
> 		return true;
>
>         if (check_loader_disabled_bsp())
>                 return true;
>
>         if (!have_cpuid_p())
>                 return true;
>
> 	return false;
>
> }
>
> and call that at the entry points and be done with it.
>
> Or if there's some other clean method to detect I'm running on a xen
> guest.
>
> Thanks.
>