linux-kernel - Re: [PATCH v2 01/11] kexec: introduce kexec

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Message-ID: <50AED7B8.7040902@citrix.com>
Date:	Fri, 23 Nov 2012 01:56:08 +0000
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Daniel Kiper <daniel.kiper@...cle.com>,
	"jbeulich@...e.com" <jbeulich@...e.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"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>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH v2 01/11] kexec: introduce kexec_ops struct

On 23/11/2012 01:38, H. Peter Anvin wrote:
> I still don't really get why it can't be isolated from dom0, which would make more sense to me, even for a Xen crash.
>

The crash region (as specified by crashkernel= on the Xen command line)
is isolated from dom0.

dom0 (using the kexec utility etc) has the task of locating the Xen
crash notes (using the kexec hypercall interface), constructing a binary
blob containing kernel, initram and gubbins, and asking Xen to put this
blob in the crash region (again, using the kexec hypercall interface).

I do not see how this is very much different from the native case
currently (although please correct me if I am misinformed).  Linux has
extra work to do by populating /proc/iomem with the Xen crash regions
boot (so the kexec utility can reference their physical addresses when
constructing the blob), and should just act as a conduit between the
kexec system call and the kexec hypercall to load the blob.

For within-guest kexec/kdump functionality, I agree that it is barking
mad.  However, we do see cloud operators interested in the idea so VM
administrators can look after their crashes themselves.

~Andrew
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