linux-kernel - Re: [patch 2/7] x86/lguest: Do not setup unused irq vectors

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Date:	Mon, 03 Aug 2015 12:17:48 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Cc:	x86@...nel.org, Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [patch 2/7] x86/lguest: Do not setup unused irq vectors

Thomas Gleixner <tglx@...utronix.de> writes:
> No point in assigning the interrupt vectors if there is no interrupt
> chip installed. Move it to lguest_setup_irq().
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> ---
>  arch/x86/lguest/boot.c |   13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> Index: tip/arch/x86/lguest/boot.c
> ===================================================================
> --- tip.orig/arch/x86/lguest/boot.c
> +++ tip/arch/x86/lguest/boot.c
> @@ -855,17 +855,13 @@ static void lguest_disable_irq(struct pc
>  
>  /*
>   * This sets up the Interrupt Descriptor Table (IDT) entry for each hardware
> - * interrupt (except 128, which is used for system calls), and then tells the
> - * Linux infrastructure that each interrupt is controlled by our level-based
> - * lguest interrupt controller.
> + * interrupt (except 128, which is used for system calls).
>   */
>  static void __init lguest_init_IRQ(void)
>  {
>  	unsigned int i;
>  
>  	for (i = FIRST_EXTERNAL_VECTOR; i < FIRST_SYSTEM_VECTOR; i++) {
> -		/* Some systems map "vectors" to interrupts weirdly.  Not us! */
> -		__this_cpu_write(vector_irq[i], i - FIRST_EXTERNAL_VECTOR);
>  		if (i != IA32_SYSCALL_VECTOR)
>  			set_intr_gate(i, irq_entries_start +
>  					8 * (i - FIRST_EXTERNAL_VECTOR));
> @@ -893,8 +889,15 @@ int lguest_setup_irq(unsigned int irq)
>  	if (err < 0 && err != -EEXIST)
>  		return err;
>  
> +	/*
> +	 * Tell the Linux infrastructure that the interrupt is
> +	 * controlled by our level-based lguest interrupt controller.
> +	 */
>  	irq_set_chip_and_handler_name(irq, &lguest_irq_controller,
>  				      handle_level_irq, "level");
> +
> +	/* Some systems map "vectors" to interrupts weirdly.  Not us! */
> +	__this_cpu_write(vector_irq[FIRST_EXTERNAL_VECTOR + irq, irq);

Missing ].

Then it doesn't work:

[    3.832028] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.832028] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.832028] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.839983] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.840026] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.840026] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.840026] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.848349] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.848349] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    3.848349] do_IRQ: 0.33 No irq handler for vector (irq -1)
[    4.056027] brd: module loaded
[    4.156025] loop: module loaded

<hit return>

[   17.712169] do_IRQ: 4 callbacks suppressed
[   17.712169] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.720462] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.720462] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.729129] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.729129] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.736523] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.736523] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.744288] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.744288] do_IRQ: 0.33 No irq handler for vector (irq -1)
[   17.751889] do_IRQ: 0.33 No irq handler for vector (irq -1)

You broke interrupts :(

Cheers,
Rusty.
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