linux-kernel - Re: [Xen-devel] [PATCH] xen/hvc-console: Make it work with HVM guests.

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Message-ID: <20131025193812.GA6256@phenom.dumpdata.com>
Date:	Fri, 25 Oct 2013 15:38:12 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	Julien Grall <julien.grall@...aro.org>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [Xen-devel] [PATCH] xen/hvc-console: Make it work with HVM
 guests.

On Thu, Oct 24, 2013 at 05:43:54PM +0100, Ian Campbell wrote:
> On Thu, 2013-10-24 at 17:30 +0100, Julien Grall wrote:
> 
> > I'm sure the solution "move xen call earlier" will come up in few mails, 
> > so there was a discussion for swiotlb few weeks ago 
> > (https://lkml.org/lkml/2013/8/29/609). And the final decision was to 
> > avoid specific Xen call in arch_setup.
> 
> It wasn't so much a hard reject as a preference based on the need
> presented at the time.
> 
> Perhaps a generic DT driven mechanism to detect hypervisors, called
> early, would be more acceptable?
> 
> > Stefano, Ian, any opinion?
> 
> The ifdef approach is a bit ugly, but if the other option doesn't work
> out I suppose we can live with it.
> 
> But stepping back how/why is this function called on x86 when not
> running under Xen? Wouldn't the use have to be using console=hvc or
> earlyprintk=xen or something -- which strikes me as user error... IOW
> can we not just nuke the check

It shouldn't - ever. On x86 it is called from the early PV bootup code.

I occasionaly use it when developing/debugging and as such want it working
in HVM even during early bootup.

> 
> Ian.
> 
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