linux-kernel - Re: [PATCH] xen: Don't call arch_trigger_all_cpu

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Date:	Mon, 01 Apr 2013 13:26:34 +0800
From:	Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Feng Jin <joe.jin@...cle.com>,
	Tamon Shiose <tamon.shiose@...cle.com>
Subject: Re: [PATCH] xen: Don't call arch_trigger_all_cpu_backtrace in dom0(pvm)


On 2013-03-29 21:46, Konrad Rzeszutek Wilk wrote:
> On Fri, Mar 29, 2013 at 03:22:38PM +0800, Zhenzhong Duan wrote:
>> nmi isn't supported in dom0, fallback to general all cpu backtrace code.
>>
>> Without fix, on xapic system, sysrq+l, no backtrace is showed.
>> On x2apic enabled system, got NULL pointer dereference as below.
> Why would the x2APIC or xAPIC make a difference here? The Linux dom0
> is not fiddling with the APIC - that is the hypervisor job.
In x2apic enabled system, dom0 kernel set apic pointer to 
apic_x2apic_cluster or apic_x2apic_phys.
When sending nmi, apic->send_IPI_all copy cpumask which isn't initialized.
For xapic system, apic->send_IPI_all=xen_send_IPI_all apic, this func 
does nothing for nmi, so no backtrace.
> Can you explain to me why x2apic_send_IPI_mask is even set? Wouldn't
> the Xen version of send_IPI be present? (See xen_smp_ops)
It's overwrited by x2apic initialization.
The problem is even without overwrite, like xapic system, 
xen_send_IPI_all doesn't work for nmi vector.
zduan
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