Re: [Fastboot] [PATCH 03/03] kexec: Avoid overwriting the current pgd (V2, x86_64)

[Magnus Damm]

On 5/26/06, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
> "Magnus Damm" <magnus.damm@xxxxxxxxx> writes:
>
> > On 5/26/06, Gerd Hoffmann <kraxel@xxxxxxx> wrote:
> >> > 1a. The C-code in xen_machine_kexec() performs a hypercall.
> >> >
> >> > 1b. The hypervisor jumps to the assembly code.
> >> > After prepare we've created a NX-safe mapping for the control page. We
> >> > jump to that NX-safe address to transfer control to the assembly code.
> >>
> >> This is about kexec'ing the physical machine, not the virtual machine,
> >> right?
> >
> > Correct, kexec:ing from dom0.
>
> And staying in dom0?  Or does Xen go away?

You replace what's running on the physical machine.

You can chose to kexec into a new "regular" Linux kernel (Xen goes
away), or kexec into a new Xen hypervisor with a new dom0 kernel (Xen
is replaced). Kexec behaves exactly the same as Linux today - no
patches are needed to kexec-tools.

Kdump is a little different though, we reserve the physical ram range
in the hypervisor and our hypervisor code is currently using a
differen format for the command line options. With Kdump under Xen it
is possible to take a memory snapshot of the entire machine - both the
hypervisor and dom0.

/ magnus
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