Re: ARM errata 430973 on multi platform kernels

[Tony Lindgren <tony@atomide.com>]

* Russell King - ARM Linux <linux@arm.linux.org.uk> [150408 16:09]:
> 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?

Boots just fine for me on n900, but let's wait for comments
from Sebastian.

Regards,

Tony
 
> > 8< --------------------
> > From: Tony Lindgren <tony@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@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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