Re: Xen 4.14.0 is busted on Dell 300x IoT Gateways

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 18 Aug 2020, Roman Shaposhnik wrote:
> Hi!
> first things first -- booting on those devices have always
> required efi=no-rs -- but it seems that Xen 4.14 is now 
> busted at a more fundamental level. I'm attaching two
> boot sequences (one with kernel 4.19.5 and one with 5.4.51)
> in the hopes that this may provide some clues right away.
> 
> Any help would be greatly appreciated!
> 
> Oh, and finally it appears that this is NOT a regression from
> Xen 4.13 -- it fails the same way. I haven't tried Xen's earlier
> than that.

FYI Roman and I tracked down the issue and it is due to the gpio
controller driver (drivers/pinctrl/intel/pinctrl-baytrail.c) overwriting
the interrupt handler data used by Xen to store the irq_data structure.

I have a very small tentative workaround, see below. It allows the
kernel to boot successfully as dom0 and gpio writes work. I am still
thinking on how to fix the issue properly in an upstreamable way, but I
wanted to send this out to the list right away in case somebody else is
stuck on this problem.


diff --git a/drivers/pinctrl/intel/pinctrl-baytrail.c 
b/drivers/pinctrl/intel/pinctrl-baytrail.c
index f38d596efa05..acd28a9e6a8a 100644
--- a/drivers/pinctrl/intel/pinctrl-baytrail.c
+++ b/drivers/pinctrl/intel/pinctrl-baytrail.c
@@ -1604,8 +1604,8 @@ static struct irq_chip byt_irqchip = {
 static void byt_gpio_irq_handler(struct irq_desc *desc)
 {
        struct irq_data *data = irq_desc_get_irq_data(desc);
-       struct byt_gpio *vg = gpiochip_get_data(
-                               irq_desc_get_handler_data(desc));
+       struct gpio_chip *gc = irq_desc_get_chip_data(desc);
+       struct byt_gpio *vg = (struct byt_gpio *)gc;
        struct irq_chip *chip = irq_data_get_irq_chip(data);
        u32 base, pin;
        void __iomem *reg;
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index a2b3d9de999c..b9551fb41ed1 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -1003,7 +1003,8 @@ irq_set_chained_handler_and_data(unsigned int irq, 
irq_flow_handler_t handle,
        if (!desc)
                return;
 
-       desc->irq_common_data.handler_data = data;
+       if (!desc->irq_common_data.handler_data)
+               desc->irq_common_data.handler_data = data;
        __irq_do_set_handler(desc, handle, 1, NULL);
 
        irq_put_desc_busunlock(desc, flags);