Re: [Xen-devel] [PATCH] x86/boot: Drop vestigial support for pre-SIPI APICs

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

On Wed, 2019-06-12 at 06:00 -0600, Jan Beulich wrote:
> > > > Reported-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> > > 
> > > Does this mean there was an actual problem resulting from this code
> > > being there, or simply the observation that this code is all dead?
> > > Clarifying one way or the other by half a sentence would be nice.
> > 
> > It was more an observation that when you kexec Xen, it blindly writes
> > into the BDA even when that wasn't set up properly by the tools.
> > 
> > Arguably that may have been kexec setup problem more than a Xen problem,
> > but after looking at this code, it is obviously that what Xen was doing
> > definitely wasn't right to do unconditionally.  It just so happens that
> > it safe to unconditionally drop the logic, rather than to make it
> > dependant on other system properties.
> > 
> > I'm not sure how best to phrase this.
> 
> Maybe "In practice issues with this were observed only with kexec"?

Not sure that's true either, is it? I found *lots* of issues when doing
kexec, and I should resend that series of boot code cleanups — but this
wasn't one of the ones I remember spotting :)

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