Messages in this thread | | | Date | Mon, 3 Nov 2008 15:01:15 -0200 | From | Eduardo Habkost <> | Subject | Re: [PATCH] Use BIOS reboot on Toshiba Portege 4000 |
| |
On Mon, Nov 03, 2008 at 08:13:07AM -0800, Eric W. Biederman wrote: > Avi Kivity <avi@redhat.com> writes: > > > Eduardo Habkost wrote: > >> We probably need to disable vmx on all CPUs, but emergency reboot skips > >> native_smp_send_stop() (where we could hook a virt_disable call in). > >> > >> As relying on IPIs defeats the whole point of emergency_restart, a proper > >> fix will need to use NMIs like the kdump code does. > >> > > > > They should use the same code; they have a similar environment at entry and > > reliability requirements for e_r are not greater than kdump's. > > Just a sec. > > I think we are confusing two issues here. > > - Ordinary machine_restart which happens to call emergency_restart. > And is proceeded by machine_shutdown. > > - And emergency_restart itself. >
I am considering only emergency_restart() itself, that simply reboots the machine. All other cases should be calling the KVM reboot notifier, that disables virtualization on all CPUs.
> To some extent I would be a lot happier if Alt-sysrq-r did what > was necessary to get into a context where it can call machine_restart > or even better kernel_restart(). > emergency_restart() is a nice idea but is broken by design.
Eliminating emergency_restart() looks good in theory, but can we eliminate it on all cases? We need something for cases when we are on a possibly-broken state and we want to reboot the machine as reliably as possible.
> > That said. If we can turn off vmx on that one processor. > That should be enough for the cpu to triple fault and let > the BIOS do what it needs to do on that cpu i.e. outb(magic, 0x92) > and toggle a motherboard level reset? > > If I read the earlier comments correctly the deep issue is > that going through ACPI to reset systems is less reliable than > doing it the classic way.
That's what Ingo suggested: instead of defaulting to ACPI reboot, disable VMX before rebooting if needed and get back to a safer default.
That leads us to the NMI stuff: we need to disable VMX on all CPUs, and we can't use IPIs if we are on a possibly-broken state.
-- Eduardo
| |