Re: [Bugfix] x86/apic: Fix xen IRQ allocation failure caused by commit b81975eade8c
From: Konrad Rzeszutek Wilk
Date: Fri Jan 09 2015 - 16:17:36 EST
On Thu, Jan 08, 2015 at 02:36:38PM +0800, Jiang Liu wrote:
> On 2015/1/7 23:44, Konrad Rzeszutek Wilk wrote:
> > On Wed, Jan 07, 2015 at 11:37:52PM +0800, Jiang Liu wrote:
> >> On 2015/1/7 22:50, Konrad Rzeszutek Wilk wrote:
> >>> On Wed, Jan 07, 2015 at 02:13:49PM +0800, Jiang Liu wrote:
> >>>> Commit b81975eade8c ("x86, irq: Clean up irqdomain transition code")
> >>>> breaks xen IRQ allocation because xen_smp_prepare_cpus() doesn't invoke
> >>>> setup_IO_APIC(), so no irqdomains created for IOAPICs and
> >>>> mp_map_pin_to_irq() fails at the very beginning.
> >>>> --- a/arch/x86/kernel/apic/io_apic.c
> >>>> +++ b/arch/x86/kernel/apic/io_apic.c
> >>>> @@ -2369,31 +2369,29 @@ static void ioapic_destroy_irqdomain(int idx)
> >>>> ioapics[idx].pin_info = NULL;
> >>>> }
> >>>>
> >>>> -void __init setup_IO_APIC(void)
> >>>> +void __init setup_IO_APIC(bool xen_smp)
> >>>> {
> >>>> int ioapic;
> >>>>
> >>>> - /*
> >>>> - * calling enable_IO_APIC() is moved to setup_local_APIC for BP
> >>>> - */
> >>>> - io_apic_irqs = nr_legacy_irqs() ? ~PIC_IRQS : ~0UL;
> >>>> + if (!xen_smp) {
> >>>> + apic_printk(APIC_VERBOSE, "ENABLING IO-APIC IRQs\n");
> >>>> + io_apic_irqs = nr_legacy_irqs() ? ~PIC_IRQS : ~0UL;
> >>>> +
> >>>> + /* Set up IO-APIC IRQ routing. */
> >>>> + x86_init.mpparse.setup_ioapic_ids();
> >>>> + sync_Arb_IDs();
> >>>> + }
> Hi Konrad,
> Enabling above code for Xen dom0 will cause following warning
> because it writes a special value to ICR register.
> [ 3.394981] ------------[ cut here ]------------
> [ 3.394985] WARNING: CPU: 0 PID: 1 at arch/x86/xen/enlighten.c:968
> xen_apic_write+0x15/0x20()
> [ 3.394988] Modules linked in:
> [ 3.394991] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.19.0-rc3+ #5
> [ 3.394993] Hardware name: Dell Inc. OptiPlex 9020/0DNKMN, BIOS A03
> 09/17/2013
> [ 3.394996] 00000000000003c8 ffff88003056bdd8 ffffffff817611bb
> 00000000000003c8
> [ 3.395000] 0000000000000000 ffff88003056be18 ffffffff8106f4ea
> 0000000000000008
> [ 3.395004] ffffffff81fc1120 ffff880030561348 000000000000a108
> 000000000000a101
> [ 3.395008] Call Trace:
> [ 3.395012] [<ffffffff817611bb>] dump_stack+0x4f/0x6c
> [ 3.395015] [<ffffffff8106f4ea>] warn_slowpath_common+0xaa/0xd0
> [ 3.395018] [<ffffffff8106f525>] warn_slowpath_null+0x15/0x20
> [ 3.395021] [<ffffffff81003e25>] xen_apic_write+0x15/0x20
> [ 3.395026] [<ffffffff81ef606b>] sync_Arb_IDs+0x84/0x86
> [ 3.395029] [<ffffffff81ef7f7a>] setup_IO_APIC+0x7f/0x8e3
> [ 3.395033] [<ffffffff810b275d>] ? trace_hardirqs_on+0xd/0x10
> [ 3.395036] [<ffffffff8176858a>] ? _raw_spin_unlock_irqrestore+0x8a/0xa0
> [ 3.395040] [<ffffffff81ee841b>] xen_smp_prepare_cpus+0x5d/0x184
> [ 3.395044] [<ffffffff81ee1ba3>] kernel_init_freeable+0x149/0x293
> [ 3.395047] [<ffffffff81758d49>] ? kernel_init+0x9/0xf0
> [ 3.395049] [<ffffffff81758d40>] ? rest_init+0xd0/0xd0
> [ 3.395052] [<ffffffff81758d49>] kernel_init+0x9/0xf0
> [ 3.395054] [<ffffffff8176887c>] ret_from_fork+0x7c/0xb0
> [ 3.395057] [<ffffffff81758d40>] ? rest_init+0xd0/0xd0
> [ 3.395066] ---[ end trace 7c4371c8ba33d5d0 ]---
>
> <snit>
> >>>> ioapic_initialized = 1;
> >>>> +
> >>>> + if (!xen_smp) {
> >>>> + init_IO_APIC_traps();
> >>>> + if (nr_legacy_irqs())
> >>>> + check_timer();
> >>>> + }
> >>>> }
> And enabling above code causes Xen dom0 reboots.
Which is due to the 'check_timer' trying to setup its timer and
failing and then moving under its feet the legacy_pic to the NULL one
and then hitting panic.
The 'check_timer' has the logic to swap the 'legacy_pic':
2186 legacy_pic->init(1);
which ends up executing:
317 new_val = inb(PIC_MASTER_IMR);
318 if (new_val != probe_val) {
319 printk(KERN_INFO "Using NULL legacy PIC\n");
320 legacy_pic = &null_legacy_pic;
321 raw_spin_unlock_irqrestore(&i8259A_lock, flags);
322 return;
323 }
And the 'legacy_pic' has now be swapped over to the 'null_legacy_pic'
for which:
2393 if (nr_legacy_irqs())
2394 check_timer();
2395
70 static inline int nr_legacy_irqs(void)
71 {
72 return legacy_pic->nr_legacy_irqs;
73 }
74
would return zero (and not invoke the 'check_timer'), but because
we do make the check inside the 'check_timer' we continue on.
Perhaps something like this?
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 3f5f604..e474389 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2184,6 +2184,14 @@ static inline void __init check_timer(void)
*/
apic_write(APIC_LVT0, APIC_LVT_MASKED | APIC_DM_EXTINT);
legacy_pic->init(1);
+ /*
+ * The init swapped out the legacy_pic to point to the NULL one.
+ * As such we should not even have entered this init routine
+ * (which depends on ->nr_legacy_irqs having an non-zero value
+ * and null_legacy_pic has zero.
+ */
+ if (legacy_pic == null_legacy_pic)
+ goto out;
pin1 = find_isa_irq_pin(0, mp_INT);
apic1 = find_isa_irq_apic(0, mp_INT);
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 4c071ae..9f404df 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -327,6 +327,7 @@ static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
xen_raw_printk(m);
panic(m);
}
+ setup_IO_APIC();
xen_init_lock_cpu(0);
smp_store_boot_cpu_info();
The patch of course ignores the WARN which woudl need something
else.
> Haven't test HVM and PV kernel yet.
> So seems we still need special treatment for xen here.
> Regards!
> Gerry
>
> >>>>
> >>>> /*
> >>>> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> >>>> index 4c071aeb8417..7eb0283901fa 100644
> >>>> --- a/arch/x86/xen/smp.c
> >>>> +++ b/arch/x86/xen/smp.c
> >>>> @@ -326,7 +326,10 @@ static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
> >>>>
> >>>> xen_raw_printk(m);
> >>>> panic(m);
> >>>> + } else {
> >>>> + setup_IO_APIC(true);
> >>>> }
> >>>> +
> >>>> xen_init_lock_cpu(0);
> >>>>
> >>>> smp_store_boot_cpu_info();
> >>>> --
> >>>> 1.7.10.4
> >>>>
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