linux-kernel - Re: [Xen-devel] [PATCH/RFC] Fix xsave bug on older Xen hypervisors

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Message-ID: <20120907145433.GA5378@phenom.dumpdata.com>
Date:	Fri, 7 Sep 2012 10:54:33 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Justin M. Forbes" <jmforbes@...uxtx.org>
Cc:	Jan Beulich <JBeulich@...e.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	Matt Wilson <msw@...zon.com>, xen-devel@...ts.xen.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH/RFC] Fix xsave bug on older Xen hypervisors

> > But iirc that bad patch is a Linux side one (i.e. you're trying to fix
> > something upstream that isn't upstream)?
> > 
> Right, so the patch that this improves upon, and that Fedora and Ubuntu are
> currently carrying is not upstream because:
> 
> a) It's crap, it cripples upstream xen users, but doesn't impact RHEL xen
> users because xsave was never supported there.
> 
> b) The hypervisor was patched to make it unnecessary quite some time ago,
> and we hoped EC2 would eventually pick up that correct patch and we could
> drop the crap kernel patch.
> 
> Unfortunately this has not happened. We are at a point where EC2 really is
> a quirk that has to be worked around. Distros do not want to maintain
> a separate EC2 build of the kernel, so the easiest way is to cripple
> current upstream xen users.  This quirk is unfortunately the best possible
> solution.  Having it upstream also makes it possible for any user to build
> an upstream kernel that will run on EC2 without having to dig a random
> patch out of a vendor kernel.

Sure. Jan is asking though for actual confirmation that the upstream kernel
does indeed go belly up without a workaround.
And whether this patch (which I would did since Canonical is carrying it) does
fix the issue.

I am still a newbie on the Amazon EC2 upload your kernel thing (hint, would
appreciate somebody taking this patch and trying it out).
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