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

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Message-Id: <50AF635B02000078000AAD0C@nat28.tlf.novell.com>
Date:	Fri, 23 Nov 2012 10:51:55 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Daniel Kiper" <daniel.kiper@...cle.com>
Cc:	"Andrew Cooper" <andrew.cooper3@...rix.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 01/11] kexec: introduce kexec_ops struct

>>> On 23.11.12 at 11:37, Daniel Kiper <daniel.kiper@...cle.com> wrote:
> On Fri, Nov 23, 2012 at 09:53:37AM +0000, Jan Beulich wrote:
>> >>> On 23.11.12 at 02:56, Andrew Cooper <andrew.cooper3@...rix.com> wrote:
>> > 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.
>>
>> But all of this _could_ be done completely independent of the
>> Dom0 kernel's kexec infrastructure (i.e. fully from user space,
>> invoking the necessary hypercalls through the privcmd driver).
> 
> No, this is impossible. kexec/kdump image lives in dom0 kernel memory
> until execution. That is why privcmd driver itself is not a solution
> in this case.

Even if so, there's no fundamental reason why that kernel image
can't be put into Xen controlled space instead.

Jan

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