Re: [Qemu-devel] [PULL 07/17] ppc: Fix rfi/rfid/hrfi/... emulation

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Jun 27, 2016 at 02:42:08PM +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2016-06-23 at 15:48 +1000, David Gibson wrote:
> > From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > 
> > This reworks emulation of the various "rfi" variants. I removed
> > some masking bits that I couldn't make sense of, the only bit that
> > I am aware we should mask here is POW, the CPU's MSR mask should
> > take care of the rest.
> 
> See I'd rather we didn't boot at all.
> 
> I just spent hours trying to figure out why my kernel wouldn't boot
> in qemu on a mac99 model with 970, weird weird things happening
> inside the device-tree parsing...
> 
> Until I figured we were losing the 64-bit mode in the MSR. Why ?
> 
> Because OpenBIOS isn't bolting the hash entries or SLBs for the entire
> kernel ! So we are taking some exceptions right during the early
> assembly, precisely between enable_64b_mode and __mmu_off.
> 
> Now this is really fishy to begin with, there is code in there that
> will use SRR0/SRR1 and won't expect a fault of any sort... such
> as __mmu_off itself.
> 
> The problem in our case was that OpenBIOS using rfi, it only restores
> 32-bits of the MSR, so we lose the 64-bit flag.
> 
> Typically that was happening on the call to __cpu_preinit_ppc970 which
> happens to reside far enough away that it needs a new translation.
> 
> I wonder if prom_init should "touch" the entire kernel for safety,
> but in any case, OpenBIOS need that fix urgently.

Ah, ok, I hadn't realized that OpenBIOS still failed to boot, just
later in the process with this hunk left out.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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