Re: IA64 kexec/kdump 2.6.18-rc5 patch

[Jack Steiner <steiner@sgi.com>]

On Tue, Sep 12, 2006 at 12:13:51PM -0500, Jack Steiner wrote:
> > Hi,
> > 	Below is the IA64 kexec/kdump patch against 2.6.18-rc5.
> > 
> ...
> > 3. put AP to a loop of hint.pause instead of call pal_halt_light.
> > diff -Nraup linux-2.6.18-rc5/arch/ia64/kernel/smp.c linux-2.6.18-rc5-kdump/arch/ia64/kernel/smp.c
> > --- linux-2.6.18-rc5/arch/ia64/kernel/smp.c	2006-06-18 09:49:35.000000000 +0800
> > +++ linux-2.6.18-rc5-kdump/arch/ia64/kernel/smp.c	2006-08-30 10:36:01.000000000 +0800
> ...
> > +void
> > +kexec_stop_this_cpu (void *func)
> > +{
> > +	unsigned long pta, impl_va_bits, pal_base;
> > +
> > +	/*
> > +	 * Remove this CPU by putting it into fake SAL rendezvous
> > +	 */
> > +	cpu_clear(smp_processor_id(), cpu_online_map);
> > +	max_xtp();
> > +	ia64_eoi();
> > +
> > +	/* Disable VHPT */
> > +	impl_va_bits = ffz(~(local_cpu_data->unimpl_va_mask | (7UL << 61)));
> > +	pta = POW2(61) - POW2(vmlpt_bits);
> > +	ia64_set_pta(pta | (0 << 8) | (vmlpt_bits << 2) | 0);
> > +
> > +	local_irq_disable();
> > +	pal_base = __get_cpu_var(ia64_mca_pal_base);
> > +	kexec_fake_sal_rendez(func, ap_wakeup_vector, pal_base);
> > +}
> > +#endif
> 
> What was the reason for introducing the kexec_fake_sal_rendez() function instead of
> actually returning to the real SAL slave loop. The HOTPLUG_CPU code in play_dead()
> in arch/ia64/kernel/process.c is very similar to what is needed.

Hmmm. I may have answered at least part of my question. It appears that the boot cpu
cannot exit back to the SAL slave loop since it was never in the slave loop to start with.

This will take some thought..... More later.


> 
> 
> I'm sure the problem is platform specific, but on the SN platform, the other cpus must be
> sent back to the real SAL slave loops. Otherwise, targeting of IO interrupts
> will not work correctly in the new kexec'd kernel. 
> 
> IO interrupts are distributed across cpus that are not in the SAL slave loop. If 
> cpus are idled in the OS instead of SAL, interrrupts are incorrected targeted
> to cpus that cannot respond.
> 
> 
> 
> -- jack