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

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:

quoted

quoted

quoted

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On 04.01.13 at 15:22, Daniel Kiper [off-list ref] wrote:

On Wed, Jan 02, 2013 at 11:26:43AM +0000, Andrew Cooper wrote:

quoted

/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