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

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

<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.

>
> 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

-- 
  Vitaly

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