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

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Date:   Fri, 16 Dec 2016 10:43:26 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Juergen Gross <jgross@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.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 Fri, Dec 16, 2016 at 10:20:42AM +0100, Juergen Gross wrote:
> Without testing, but I doubt it is working. As pv guests aren't coming
> through check_loader_disabled_bsp() at all I can't see why your patch
> would work for dom0.

Do they go through check_loader_disabled_ap() ?

> Additionally I don't think you want to call native_cpuid() if
> have_cpuid_p() returns false.

Good point, fixed.

> So I think you want a generic "platform_allows_ucode_load()"
> function checking for support of cpuid and virtualization. This
> function should be called both in check_loader_disabled_bsp() and
> check_loader_disabled_ap() to bail out early.

See question above. If they go through check_loader_disabled_ap(),
then I'm inclined to set dis_ucode_ldr to true at build time and let
check_loader_disabled_bsp() set it to false on baremetal or if any of
the other checks pass.

If the pv guests run into check_loader_disabled_ap, then they'll see
dis_ucode_ldr true and return.

Ok?

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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