[PATCH] Fix PMU + soft interrupt disable bug

[Benjamin Herrenschmidt]

On Sun, 2008-03-16 at 23:27 -0500, Anton Blanchard wrote:
> Since the PMU is an NMI now, it can come at any time we are only soft
> disabled. We must hard disable around the two places we allow the kernel
> stack SLB and r1 to go out of sync. Otherwise the PMU exception can
> force a kernel stack SLB into another slot.
> 
> Signed-off-by: Anton Blanchard <anton at samba.org>

Acked-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
---

> ---
> 
> Index: kernel/arch/powerpc/mm/slb.c
> ===================================================================
> --- kernel.orig/arch/powerpc/mm/slb.c	2007-11-05 11:22:03.000000000 -0600
> +++ kernel/arch/powerpc/mm/slb.c	2007-11-05 18:09:45.000000000 -0600
> @@ -113,6 +113,12 @@ void slb_flush_and_rebolt(void)
>  		slb_shadow_update(get_paca()->kstack, lflags, 2);
>  	}
>  
> +	/*
> +	 * We can't take a PMU exception in the following code, so hard
> +	 * disable interrupts.
> +	 */
> +	hard_irq_disable();
> +
>  	/* We need to do this all in asm, so we're sure we don't touch
>  	 * the stack between the slbia and rebolting it. */
>  	asm volatile("isync\n"
> Index: kernel/arch/powerpc/kernel/process.c
> ===================================================================
> --- kernel.orig/arch/powerpc/kernel/process.c	2007-11-05 18:10:44.000000000 -0600
> +++ kernel/arch/powerpc/kernel/process.c	2007-11-05 18:10:46.000000000 -0600
> @@ -331,6 +331,12 @@ struct task_struct *__switch_to(struct t
>  	account_process_vtime(current);
>  	calculate_steal_time();
>  
> +	/*
> +	 * We can't take a PMU exception inside _switch() since there is a
> +	 * window where the kernel stack SLB and the kernel stack are out
> +	 * of sync. Hard disable here.
> +	 */
> +	hard_irq_disable();
>  	last = _switch(old_thread, new_thread);
>  
>  	local_irq_restore(flags);
> 
> 
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