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

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Message-ID: <20141127162118.GA24829@konrad-lan.dumpdata.com>
Date:	Thu, 27 Nov 2014 11:21:19 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Boris Ostrovsky <boris.ostrovsky@...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 Thu, Nov 27, 2014 at 10:12:28AM +0100, Borislav Petkov wrote:
> 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.

You are describing 'paravirt_enabled()' :-)
> 
> 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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