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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

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@oracle.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.

> 
> Daniel