linux-kernel - Re: [PATCH] ARM: fix alignement of __bug

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Message-ID: <20150906194805.GP21084@n2100.arm.linux.org.uk>
Date:	Sun, 6 Sep 2015 20:48:06 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:	Dave Martin <Dave.Martin@....com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: fix alignement of __bug_table section entries

On Sun, Sep 06, 2015 at 07:25:01PM +0200, Robert Jarzmik wrote:
> Russell King - ARM Linux <linux@....linux.org.uk> writes:
> 
> > On Sat, Sep 05, 2015 at 07:10:49PM +0200, Robert Jarzmik wrote:
> >> Russell King - ARM Linux <linux@....linux.org.uk> writes:
> >> So the issue is around this SW_DOMAIN_PAN, at least on PXA.
> >
> > If so, you may need to add:
> >
> > 	mrc p15, 0, \rd, c2, c0, 0
> > 	mov \rd, \rd
> > 	sub pc, pc, #4
> >
> > to the places we update the domain access register to ensure that the
> > Xscale pipeline stalls to allow the CP15 DACR update to hit.
> Nope, that didn't work.
> I have tried 2 different patches :
>  - in [1], your proposed solution
>  - in [2], a PrefetchFlush as adviced by ARM Architecture Reference Manual
> 
> None of them worked. I confirmed by disassembling __dabt_svc my changes hit the
> abort routine, and they did. I'll continue next week by trying to have a closer
> look at the SW_DOMAIN_PAN commit (a5e090acbf545), and take time to walk through
> the whole Oops for information I have missed.
> 
> Cheers.
> 
> -- 
> Robert
> 
> [1] Approach 1 : translation table sync
> =======================================
> diff --cc arch/arm/include/asm/assembler.h
> index 7bbf325a4f31,7bbf325a4f31..6bb46198fd08
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@@ -449,6 -449,6 +449,12 @@@ THUMB(    orr     \reg , \reg , #PSR_T_BIT        
>   #endif
>         .endm
>   
> ++      .macro  dacr_sync, rd
> ++      mrc     p15, 0, \rd, c2, c0, 0
> ++      mov     \rd, \rd
> ++      sub     pc, pc, #4
> ++      .endm
> ++
>         .macro  uaccess_disable, tmp, isb=1
>   #ifdef CONFIG_CPU_SW_DOMAIN_PAN
>         /*
> @@@ -457,6 -457,6 +463,7 @@@
>          */
>         mov     \tmp, #DACR_UACCESS_DISABLE
>         mcr     p15, 0, \tmp, c3, c0, 0         @ Set domain register
> ++      dacr_sync \tmp
>         .if     \isb
>         instr_sync
>         .endif
> @@@ -471,6 -471,6 +478,7 @@@
>          */
>         mov     \tmp, #DACR_UACCESS_ENABLE
>         mcr     p15, 0, \tmp, c3, c0, 0
> ++      dacr_sync \tmp
>         .if     \isb
>         instr_sync
>         .endif
> @@@ -488,6 -488,6 +496,7 @@@
>   #ifdef CONFIG_CPU_SW_DOMAIN_PAN
>         ldr     r0, [sp, #S_FRAME_SIZE]
>         mcr     p15, 0, r0, c3, c0, 0
> ++      dacr_sync r0
>   #endif
>         .endm

The important place is in arch/arm/include/asm/domain.h, which is where
we manipulate the DACR within probe_kernel_address().

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