linux-kernel - Re: [PATCH 3.17 100/141] x86, microcode: Fix accessing dis_ucode

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Date:	Thu, 27 Nov 2014 10:12:28 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	konrad.wilk@...cle.com, x86@...nel.org, gregkh@...uxfoundation.org,
	david.vrabel@...rix.com, stable@...r.kernel.org,
	rshendershot@...si.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3.17 100/141] x86, microcode: Fix accessing dis_ucode_ldr
 on 32-bit

On Wed, Nov 26, 2014 at 07:13:02PM -0800, Boris Ostrovsky wrote:
> I was confusing you: accessing dis_ucode_ldr by virtual address does
> work on PV. But we then fail later, in load_ucode_intel_ap(), because
> it also tries to use __pa_nodebug() which can't be used by PV.
>
> So if accessing dis_ucode_ldr by virtual address is acceptable
> (although I don't think it is?) then we can stick dis_ucode_ldr=1 into
> xen_start_kernel() and then things look OK.
>
> A better solution may be to replace cpuid in x86_guest() with 'return
> pv_info.paravirt_enabled' (or paravirt_enabled(), I guess). I gave
> it a quick spin (32-bit only) and it seems to work. I'll see how my
> overnight tests behave.

Ok, but let's have a clean design: maybe have a weak default stub which
returns false when PARAVIRT is not enabled in the .config and then add
an override in, say, arch/x86/kernel/paravirt.c which returns true when
running as a guest. Something like that, at least.

I can imagine other stuff wanting to use the dynamic checking at runtime
too...

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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