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

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Message-ID: <20130107123404.GA2927@host-192-168-1-59.local.net-space.pl>
Date:	Mon, 7 Jan 2013 13:34:04 +0100
From:	Daniel Kiper <daniel.kiper@...cle.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	Jan Beulich <JBeulich@...e.com>,
	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>,
	"maxim.uvarov@...cle.com" <maxim.uvarov@...cle.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"vgoyal@...hat.com" <vgoyal@...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: [Xen-devel] [PATCH v3 00/11] xen: Initial kexec/kdump
 implementation

On Fri, Jan 04, 2013 at 02:11:46PM -0500, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 04, 2013 at 06:07:51PM +0100, Daniel Kiper wrote:
> > On Fri, Jan 04, 2013 at 02:41:17PM +0000, Jan Beulich wrote:
> > > >>> On 04.01.13 at 15:22, Daniel Kiper <daniel.kiper@...cle.com> wrote:
> > > > On Wed, Jan 02, 2013 at 11:26:43AM +0000, Andrew Cooper wrote:
> > > >> /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.
> > >
> > > Why?
> >
> > Because current KEXEC_CMD_kexec_load does not load kernel
> > image and other things into Xen memory. It means that it
> > should live somewhere in dom0 Linux kernel memory.
>
> We could have a very simple hypercall which would have:
>
> struct fancy_new_hypercall {
> 	xen_pfn_t payload; // IN
> 	ssize_t len; // IN
> #define DATA (1<<1)
> #define DATA_EOF (1<<2)
> #define DATA_KERNEL (1<<3)
> #define DATA_RAMDISK (1<<4)
> 	unsigned int flags; // IN
> 	unsigned int status; // OUT
> };
>
> which would in a loop just iterate over the payloads and
> let the hypervisor stick it in the crashkernel space.
>
> This is all hand-waving of course. There probably would be a need
> to figure out how much space you have in the reserved Xen's
> 'crashkernel' memory region too.

I think that new kexec hypercall function should mimics kexec syscall.
It means that all arguments passed to hypercall should have same types
if it is possible or if it is not possible then conversion should be done
in very easy way. Additionally, I think that one call of new hypercall
load function should load all needed thinks in right place and
return relevant status. Last but not least, new functionality should
be available through /dev/xen/privcmd or directly from kernel without
bigger effort.

Daniel
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