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

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Date:	Fri, 4 Jan 2013 18:01:20 +0100
From:	Daniel Kiper <daniel.kiper@...cle.com>
To:	David Vrabel <david.vrabel@...rix.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, Jan 04, 2013 at 02:38:44PM +0000, David Vrabel wrote:
> On 04/01/13 14:22, 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.
>
> I don't see why the hypercall ABI cannot be extended with new sub-ops
> that do the right thing -- the existing ABI is a bit weird.
>
> I plan to start prototyping something shortly (hopefully next week) for
> the Xen kexec case.

Wow... As I can this time Xen community is interested in...
That is great. I agree that current kexec interface is not ideal.

David, I am happy to help in that process. However, if you wish I could
carry it myself. Anyway, it looks that I should hold on with my
Linux kexec/kdump patches.

My .5 cents:
  - We should focus on KEXEC_CMD_kexec_load and KEXEC_CMD_kexec_unload;
    probably we should introduce KEXEC_CMD_kexec_load2 and KEXEC_CMD_kexec_unload2;
    load should __LOAD__ kernel image and other things into hypervisor memory;
    I suppose that allmost all things could be copied from linux/kernel/kexec.c,
    linux/arch/x86/kernel/{machine_kexec_$(BITS).c,relocate_kernel_$(BITS).c};
    I think that KEXEC_CMD_kexec should stay as is,
  - Hmmm... Now I think that we should still use kexec syscall to load image
    into Xen memory (with new KEXEC_CMD_kexec_load2) because it establishes
    all things which are needed to call kdump if dom0 crashes; however,
    I could be wrong...
  - last but not least, we should think about support for PV guests too.

Daniel
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