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

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Message-ID: <20121123103726.GB2921@host-192-168-1-59.local.net-space.pl>
Date:	Fri, 23 Nov 2012 11:37:26 +0100
From:	Daniel Kiper <daniel.kiper@...cle.com>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	Andrew Cooper <andrew.cooper3@...rix.com>,
	"H. Peter Anvin" <hpa@...or.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>
Subject: Re: [PATCH v2 01/11] kexec: introduce kexec_ops struct

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.

> It's just that parts of the kexec infrastructure can be re-used
> (and hence that mechanism probably seemed the easier approach
> to the implementer of the original kexec-on-Xen). If the kernel
> folks dislike that re-use (quite understandably looking at how
> much of it needs to be re-done), that shouldn't prevent us from
> looking into the existing alternatives.

This is last resort option. First I think we should try to find
good solution which reuses existing code as much as possible.

Daniel
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