linux-kernel - Re: [Xen-devel] [PATCH v3 00/11] xen: Initial kexec/kdump implementation

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Message-ID: <1357310073.14291.42.camel@zakaz.uk.xensource.com>
Date:	Fri, 4 Jan 2013 14:34:33 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Daniel Kiper <daniel.kiper@...cle.com>
CC:	Andrew Cooper <Andrew.Cooper3@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"maxim.uvarov@...cle.com" <maxim.uvarov@...cle.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"jbeulich@...e.com" <jbeulich@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>
Subject: Re: [Xen-devel] [PATCH v3 00/11] xen: Initial kexec/kdump
 implementation

On Fri, 2013-01-04 at 14:22 +0000, Daniel Kiper wrote:
> On Wed, Jan 02, 2013 at 11:26:43AM +0000, Andrew Cooper wrote:
> > On 27/12/12 18:02, Eric W. Biederman wrote:
> > >Andrew Cooper<andrew.cooper3@...rix.com>  writes:
> > >
> > >>On 27/12/2012 07:53, Eric W. Biederman wrote:
> > >>>The syscall ABI still has the wrong semantics.
> > >>>
> > >>>Aka totally unmaintainable and umergeable.
> > >>>
> > >>>The concept of domU support is also strange.  What does domU support even mean, when the dom0 support is loading a kernel to pick up Xen when Xen falls over.
> > >>There are two requirements pulling at this patch series, but I agree
> > >>that we need to clarify them.
> > >It probably make sense to split them apart a little even.
> > >
> > >
> >
> > Thinking about this split, there might be a way to simply it even more.
> >
> > /sbin/kexec can load the "Xen" crash kernel itself by issuing
> > hypercalls using /dev/xen/privcmd.  This would remove the need for
> > the dom0 kernel to distinguish between loading a crash kernel for
> > itself and loading a kernel for Xen.
> >
> > Or is this just a silly idea complicating the matter?
> 
> This is impossible with current Xen kexec/kdump interface.
> It should be changed to do that. However, I suppose that
> Xen community would not be interested in such changes.

The current HYPERVISOR_kexec interface is pretty fricken bad (it
basically hardcodes the Linux Circa-2.6.18 internal interface!).

I'd be all for a new HYPERVISOR_kexec (with the old gaining a _compat
suffix) which implements something more generic that isn't tied to a
particular dom0 kernel implementation (be it differing versions of Linux
or e.g. *BSD).

If that enables /sbin/kexec to load the kernel directly then so much the
better, assuming the /sbin/kexec maintainers are happy with that
approach.

Ian.

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