ARM errata 430973 on multi platform kernels

[Russell King - ARM Linux]

On Tue, Apr 07, 2015 at 08:44:05AM -0700, Tony Lindgren wrote:
> And then on top of that patch, we can fix the sefaulting issues with the
> following, what do you guys think?

Has this change been tested on OMAP secure parts?

> 8< --------------------
> From: Tony Lindgren <tony at atomide.com>
> Date: Tue, 7 Apr 2015 07:52:39 -0700
> Subject: [PATCH] ARM: mm: Fix Cortex-A8 erratum 430973 segfaults for bootloaders and multiarch
> 
> Looks like apps can be made to segfault easily on armhf distros
> just by running cpuburn-a8 in the background, then starting apt
> get update unless erratum 430973 workaround is enabled. This happens
> on r3p2 also, which has 430973 fixed in hardware.
> 
> Turns out the reason for this is some bootloaders incorrectly
> setting the auxilary register IBE bit, which probably causes us
> to hit erratum 687067 on Cortex-A8 later than r1p2.
> 
> Now that Cortex-A8 has it's own cpu_ca8_switch_mm, we can fix these
> issues:
> 
> 1. If the bootloader incorrectly sets the IBE bit in the auxilary
>    control register for Cortex-A8 revisions with 430973 fixed
>    in hardware, we need to call flush BTAC/BTB to avoid segfaults
>    probably caused by erratum 687067. So let's flush BTAC/BTB
>    unconditionally for Cortex-A8. It won't do anything unless the
>    IBE bit is set.
> 
> 2. We can and should now keep 430973 enabled for multiarch builds
>    as it no longer causes issues with Cortex-A9 as we have a separate
>    cpu_ca8_switch_mm.
> 
> Note that SoCs probably should also add checks and print warnings
> for the misconfigured IBE bit depending on the Cortex-A8 revision
> so the bootloaders can be fixed Cortex-A8 revisions later than
> r1p2 to not set the IBE bit.
> 
> Signed-off-by: Tony Lindgren <tony at atomide.com>
> 
> --- a/arch/arm/mm/proc-v7-2level.S
> +++ b/arch/arm/mm/proc-v7-2level.S
> @@ -36,14 +36,16 @@
>   *
>   *	It is assumed that:
>   *	- we are not using split page tables
> + *
> + *	Note that we always need to flush BTAC/BTB if IBE is set
> + *	even on Cortex-A8 revisions not affected by 430973.
> + *	If IBE is not set, the flush BTAC/BTB won't do anything.
>   */
>  ENTRY(cpu_ca8_switch_mm)
>  #ifdef CONFIG_MMU
>  	mov	r2, #0
> -#ifdef CONFIG_ARM_ERRATA_430973
>  	mcr	p15, 0, r2, c7, c5, 6		@ flush BTAC/BTB
>  #endif
> -#endif
>  ENTRY(cpu_v7_switch_mm)
>  #ifdef CONFIG_MMU
>  	mmid	r1, r1				@ get mm->context.id
> --- a/arch/arm/mm/proc-v7.S
> +++ b/arch/arm/mm/proc-v7.S
> @@ -352,7 +352,7 @@ __v7_setup:
>  	ldr	r10, =0x00000c08		@ Cortex-A8 primary part number
>  	teq	r0, r10
>  	bne	2f
> -#if defined(CONFIG_ARM_ERRATA_430973) && !defined(CONFIG_ARCH_MULTIPLATFORM)
> +#if defined(CONFIG_ARM_ERRATA_430973)
>  
>  	teq	r5, #0x00100000			@ only present in r1p*
>  	mrceq	p15, 0, r10, c1, c0, 1		@ read aux control register

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