Subject: [PATCH] ARM: protect usage of cr_alignment by #ifdef CONFIG_CPU_CP15

From: [email-masked] (Ryan Mallon)
Date: Thu, 19 Jan 2012 08:39:08 +1100

On 17/01/12 03:49, Uwe Kleine-K?nig wrote:

> cr_alignment is defined in arch/arm/kernel/entry-armv.S. When a build
> doesn't include this file but arch/arm/kernel/head-common.S the latter
> intruduces an invalid reference to cr_alignment.
> 
> So handle cr_alignment not being available in head-common.S and for
> completeness only define and use cr_alignment (and cr_no_alignment) when
> CONFIG_CPU_CP15 is enabled.
> 
> Signed-off-by: Uwe Kleine-K?nig <[email-masked]>

Hi Uwe,

We have something similar to this patch for our para-virtualised Linux
kernel (www.ok-labs.com). I agree with Russell that we need a user of
this code in the kernel before making this change, and our own patches
are in no danger of hitting mainline any time soon, but I would like to
see this patch go in.

One minor comment below.

Thanks,
~Ryan

> ---
> Hello,
> 
> currently arch/arm/kernel/entry-armv.S is used unconditionally, but the
> Cortex-M3 port in my tree doesn't need it. So this patch fixex a build
> error only in my tree and it's not urgent to include it.
> 
> Best regards
> Uwe
> 
>  arch/arm/include/asm/system.h |    2 ++
>  arch/arm/kernel/entry-armv.S  |    4 ++++
>  arch/arm/kernel/head-common.S |    9 +++++++--
>  arch/arm/kernel/setup.c       |    8 ++++++--
>  arch/arm/mm/alignment.c       |    6 ++++++
>  arch/arm/mm/mmu.c             |    8 +++++++-
>  6 files changed, 32 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
> index 984014b..54c9921 100644
> --- a/arch/arm/include/asm/system.h
> +++ b/arch/arm/include/asm/system.h
> @@ -177,6 +177,7 @@ extern unsigned int user_debug;
>  #define set_mb(var, value)	do { var = value; smp_mb(); } while (0)
>  #define nop() __asm__ __volatile__("mov\tr0,r0\t@ nop\n\t");

There is another reference in this file to cr_alignment:

#if __LINUX_ARM_ARCH__ >= 4
#define vectors_high()  (cr_alignment & CR_V)
#else
#define vectors_high()  (0)
#endif

In our para-virtualised kernel we hardcode the value of vectors_high()
to 1, however this is might not be the correct thing to do universally
if !CONFIG_CPU_CP15 && __LINUX_ARM_ARCH__ >= 4.

>  
> +#ifdef CONFIG_CPU_CP15
>  extern unsigned long cr_no_alignment;	/* defined in entry-armv.S */
>  extern unsigned long cr_alignment;	/* defined in entry-armv.S */
>  
> @@ -216,6 +217,7 @@ static inline void set_copro_access(unsigned int val)
>  	  : : "r" (val) : "cc");
>  	isb();
>  }
> +#endif
>  
>  /*
>   * switch_mm() may do a full cache flush over the context switch,
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index b145f16..7782e7d 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -315,8 +315,10 @@ __pabt_svc:
>  ENDPROC(__pabt_svc)
>  
>  	.align	5
> +#ifdef CONFIG_CPU_CP15
>  .LCcralign:
>  	.word	cr_alignment
> +#endif
>  #ifdef MULTI_DABORT
>  .LCprocfns:
>  	.word	processor
> @@ -1147,12 +1149,14 @@ __vectors_end:
>  
>  	.data
>  
> +#ifdef CONFIG_CPU_CP15
>  	.globl	cr_alignment
>  	.globl	cr_no_alignment
>  cr_alignment:
>  	.space	4
>  cr_no_alignment:
>  	.space	4
> +#endif
>  
>  #ifdef CONFIG_MULTI_IRQ_HANDLER
>  	.globl	handle_arch_irq
> diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
> index 854bd22..2f560c5 100644
> --- a/arch/arm/kernel/head-common.S
> +++ b/arch/arm/kernel/head-common.S
> @@ -98,8 +98,9 @@ __mmap_switched:
>  	str	r9, [r4]			@ Save processor ID
>  	str	r1, [r5]			@ Save machine type
>  	str	r2, [r6]			@ Save atags pointer
> -	bic	r4, r0, #CR_A			@ Clear 'A' bit
> -	stmia	r7, {r0, r4}			@ Save control register values
> +	cmp	r7, #0
> +	bicne	r4, r0, #CR_A			@ Clear 'A' bit
> +	stmneia	r7, {r0, r4}			@ Save control register values
>  	b	start_kernel
>  ENDPROC(__mmap_switched)
>  
> @@ -113,7 +114,11 @@ __mmap_switched_data:
>  	.long	processor_id			@ r4
>  	.long	__machine_arch_type		@ r5
>  	.long	__atags_pointer			@ r6
> +#ifdef CONFIG_CPU_CP15
>  	.long	cr_alignment			@ r7
> +#else
> +	.long	0
> +#endif
>  	.long	init_thread_union + THREAD_START_SP @ sp
>  	.size	__mmap_switched_data, . - __mmap_switched_data
>  
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 8fc2c8f..d37a02fa 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -457,9 +457,13 @@ static void __init setup_processor(void)
>  	cpu_cache = *list->cache;
>  #endif
>  
> -	printk("CPU: %s [%08x] revision %d (ARMv%s), cr=%08lx\n",
> +	printk("CPU: %s [%08x] revision %d (ARMv%s)",
>  	       cpu_name, read_cpuid_id(), read_cpuid_id() & 15,
> -	       proc_arch[cpu_architecture()], cr_alignment);
> +	       proc_arch[cpu_architecture()]);
> +
> +#ifdef CONFIG_CPU_CP15
> +	printk(KERN_CONT ", cr=%08lx\n", cr_alignment);
> +#endif
>  
>  	snprintf(init_utsname()->machine, __NEW_UTS_LEN + 1, "%s%c",
>  		 list->arch_name, ENDIANNESS);
> diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
> index c335c76..56da01c 100644
> --- a/arch/arm/mm/alignment.c
> +++ b/arch/arm/mm/alignment.c
> @@ -89,7 +89,11 @@ core_param(alignment, ai_usermode, int, 0600);
>  /* Return true if and only if the ARMv6 unaligned access model is in use. */
>  static bool cpu_is_v6_unaligned(void)
>  {
> +#ifdef CONFIG_CPU_CP15
>  	return cpu_architecture() >= CPU_ARCH_ARMv6 && (cr_alignment & CR_U);
> +#else
> +	return 0;
> +#endif
>  }
>  
>  static int safe_usermode(int new_usermode, bool warn)
> @@ -961,12 +965,14 @@ static int __init alignment_init(void)
>  		return -ENOMEM;
>  #endif
>  
> +#ifdef CONFIG_CPU_CP15
>  	if (cpu_is_v6_unaligned()) {
>  		cr_alignment &= ~CR_A;
>  		cr_no_alignment &= ~CR_A;
>  		set_cr(cr_alignment);
>  		ai_usermode = safe_usermode(ai_usermode, false);
>  	}
> +#endif
>  
>  	hook_fault_code(1, do_alignment, SIGBUS, BUS_ADRALN,
>  			"alignment exception");
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 8b8446a..d5a170a 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -106,8 +106,10 @@ static int __init early_cachepolicy(char *p)
>  	for (i = 0; i < ARRAY_SIZE(cache_policies); i++) {
>  		if (strcmp(p, cache_policies[i].policy) == 0) {
>  			cachepolicy = i;
> +#ifdef CONFIG_CPU_CP15
>  			cr_alignment &= ~cache_policies[i].cr_mask;
>  			cr_no_alignment &= ~cache_policies[i].cr_mask;
> +#endif
>  			break;
>  		}
>  	}
> @@ -125,7 +127,9 @@ static int __init early_cachepolicy(char *p)
>  		cachepolicy = CPOLICY_WRITEBACK;
>  	}
>  	flush_cache_all();
> +#ifdef CONFIG_CPU_CP15
>  	set_cr(cr_alignment);
> +#endif
>  	return 0;
>  }
>  early_param("cachepolicy", early_cachepolicy);
> @@ -158,6 +162,7 @@ static int __init early_ecc(char *p)
>  }
>  early_param("ecc", early_ecc);
>  
> +#ifdef CONFIG_CPU_CP15
>  static int __init noalign_setup(char *__unused)
>  {
>  	cr_alignment &= ~CR_A;
> @@ -166,8 +171,9 @@ static int __init noalign_setup(char *__unused)
>  	return 1;
>  }
>  __setup("noalign", noalign_setup);
> +#endif
>  
> -#ifndef CONFIG_SMP
> +#if !defined(CONFIG_SMP) && defined(CONFIG_CPU_CP15)
>  void adjust_cr(unsigned long mask, unsigned long set)
>  {
>  	unsigned long flags;