Re: [Xen-devel] Patch "x86/irq: Probe for PIC presence before allocating descs for legacy IRQs" has been added to the 4.3-stable tree

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Monday, December 7, 2015, 1:54:35 PM, you wrote:

> <gregkh@xxxxxxxxxxxxxxxxxxx> writes:

>> This is a note to let you know that I've just added the patch titled
>>
>>     x86/irq: Probe for PIC presence before allocating descs for legacy IRQs
>>
>> to the 4.3-stable tree which can be found at:
>>     
>> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>>
>> The filename of the patch is:
>>      
>> x86-irq-probe-for-pic-presence-before-allocating-descs-for-legacy-irqs.patch
>> and it can be found in the queue-4.3 subdirectory.
>>
>> If you, or anyone else, feels it should not be added to the stable tree,
>> please let <stable@xxxxxxxxxxxxxxx> know about it.

> This commit is known for breaking Xen PV guests, the breakage is fixed
> with the following:

> commit b4ff8389ed14b849354b59ce9b360bdefcdbf99c
> Author: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Date:   Fri Nov 20 11:25:04 2015 -0500

>     xen/events: Always allocate legacy interrupts on PV guests

> I suggest we include this commit as well. Same for 4.2-stable tree.

Which in turn causes the problem described in:
"Xen-devel] [PATCHv1] x86: rtc_cmos platform device requires legacy irqs"
http://lkml.iu.edu/hypermail/linux/kernel/1512.0/02430.html

for which a patch is still pending a discussion about the right way to fix it.

--
Sander

>>
>> From 8c058b0b9c34d8c8d7912880956543769323e2d8 Mon Sep 17 00:00:00 2001
>> From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>> Date: Tue, 3 Nov 2015 10:40:14 +0100
>> Subject: x86/irq: Probe for PIC presence before allocating descs for legacy 
>> IRQs
>>
>> From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>>
>> commit 8c058b0b9c34d8c8d7912880956543769323e2d8 upstream.
>>
>> Commit d32932d02e18 ("x86/irq: Convert IOAPIC to use hierarchical irqdomain
>> interfaces") brought a regression for Hyper-V Gen2 instances. These
>> instances don't have i8259 legacy PIC but they use legacy IRQs for serial
>> port, rtc, and acpi. With this commit included we end up with these IRQs
>> not initialized. Earlier, there was a special workaround for legacy IRQs
>> in mp_map_pin_to_irq() doing mp_irqdomain_map() without looking at
>> nr_legacy_irqs() and now we fail in __irq_domain_alloc_irqs() when
>> irq_domain_alloc_descs() returns -EEXIST.
>>
>> The essence of the issue seems to be that early_irq_init() calls
>> arch_probe_nr_irqs() to figure out the number of legacy IRQs before
>> we probe for i8259 and gets 16. Later when init_8259A() is called we switch
>> to NULL legacy PIC and nr_legacy_irqs() starts to return 0 but we already
>> have 16 descs allocated.
>>
>> Solve the issue by separating i8259 probe from init and calling it in
>> arch_probe_nr_irqs() before we actually use nr_legacy_irqs() information.
>>
>> Fixes: d32932d02e18 ("x86/irq: Convert IOAPIC to use hierarchical irqdomain 
>> interfaces")
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>> Cc: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
>> Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
>> Link: 
>> http://lkml.kernel.org/r/1446543614-3621-1-git-send-email-vkuznets@xxxxxxxxxx
>> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>>
>> ---
>>  arch/x86/include/asm/i8259.h  |    1 +
>>  arch/x86/kernel/apic/vector.c |    6 +++++-
>>  arch/x86/kernel/i8259.c       |   29 +++++++++++++++++++++--------
>>  3 files changed, 27 insertions(+), 9 deletions(-)
>>
>> --- a/arch/x86/include/asm/i8259.h
>> +++ b/arch/x86/include/asm/i8259.h
>> @@ -60,6 +60,7 @@ struct legacy_pic {
>>       void (*mask_all)(void);
>>       void (*restore_mask)(void);
>>       void (*init)(int auto_eoi);
>> +     int (*probe)(void);
>>       int (*irq_pending)(unsigned int irq);
>>       void (*make_irq)(unsigned int irq);
>>  };
>> --- a/arch/x86/kernel/apic/vector.c
>> +++ b/arch/x86/kernel/apic/vector.c
>> @@ -361,7 +361,11 @@ int __init arch_probe_nr_irqs(void)
>>       if (nr < nr_irqs)
>>               nr_irqs = nr;
>>
>> -     return nr_legacy_irqs();
>> +     /*
>> +      * We don't know if PIC is present at this point so we need to do
>> +      * probe() to get the right number of legacy IRQs.
>> +      */
>> +     return legacy_pic->probe();
>>  }
>>
>>  #ifdef       CONFIG_X86_IO_APIC
>> --- a/arch/x86/kernel/i8259.c
>> +++ b/arch/x86/kernel/i8259.c
>> @@ -295,16 +295,11 @@ static void unmask_8259A(void)
>>       raw_spin_unlock_irqrestore(&i8259A_lock, flags);
>>  }
>>
>> -static void init_8259A(int auto_eoi)
>> +static int probe_8259A(void)
>>  {
>>       unsigned long flags;
>>       unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
>>       unsigned char new_val;
>> -
>> -     i8259A_auto_eoi = auto_eoi;
>> -
>> -     raw_spin_lock_irqsave(&i8259A_lock, flags);
>> -
>>       /*
>>        * Check to see if we have a PIC.
>>        * Mask all except the cascade and read
>> @@ -312,16 +307,28 @@ static void init_8259A(int auto_eoi)
>>        * have a PIC, we will read 0xff as opposed to the
>>        * value we wrote.
>>        */
>> +     raw_spin_lock_irqsave(&i8259A_lock, flags);
>> +
>>       outb(0xff, PIC_SLAVE_IMR);      /* mask all of 8259A-2 */
>>       outb(probe_val, PIC_MASTER_IMR);
>>       new_val = inb(PIC_MASTER_IMR);
>>       if (new_val != probe_val) {
>>               printk(KERN_INFO "Using NULL legacy PIC\n");
>>               legacy_pic = &null_legacy_pic;
>> -             raw_spin_unlock_irqrestore(&i8259A_lock, flags);
>> -             return;
>>       }
>>
>> +     raw_spin_unlock_irqrestore(&i8259A_lock, flags);
>> +     return nr_legacy_irqs();
>> +}
>> +
>> +static void init_8259A(int auto_eoi)
>> +{
>> +     unsigned long flags;
>> +
>> +     i8259A_auto_eoi = auto_eoi;
>> +
>> +     raw_spin_lock_irqsave(&i8259A_lock, flags);
>> +
>>       outb(0xff, PIC_MASTER_IMR);     /* mask all of 8259A-1 */
>>
>>       /*
>> @@ -379,6 +386,10 @@ static int legacy_pic_irq_pending_noop(u
>>  {
>>       return 0;
>>  }
>> +static int legacy_pic_probe(void)
>> +{
>> +     return 0;
>> +}
>>
>>  struct legacy_pic null_legacy_pic = {
>>       .nr_legacy_irqs = 0,
>> @@ -388,6 +399,7 @@ struct legacy_pic null_legacy_pic = {
>>       .mask_all = legacy_pic_noop,
>>       .restore_mask = legacy_pic_noop,
>>       .init = legacy_pic_int_noop,
>> +     .probe = legacy_pic_probe,
>>       .irq_pending = legacy_pic_irq_pending_noop,
>>       .make_irq = legacy_pic_uint_noop,
>>  };
>> @@ -400,6 +412,7 @@ struct legacy_pic default_legacy_pic = {
>>       .mask_all = mask_8259A,
>>       .restore_mask = unmask_8259A,
>>       .init = init_8259A,
>> +     .probe = probe_8259A,
>>       .irq_pending = i8259A_irq_pending,
>>       .make_irq = make_8259A_irq,
>>  };
>>
>> Patches currently in stable-queue which might be from vkuznets@xxxxxxxxxx are
>>
>> queue-4.3/x86-irq-probe-for-pic-presence-before-allocating-descs-for-legacy-irqs.patch



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