[PATCH 2/3] arm: virt: ensure visibility of __boot_cpu_mode

[Dave.Martin@arm.com (Dave Martin)]

On Tue, Jul 09, 2013 at 03:16:05PM +0100, Mark Rutland wrote:
> Secondary CPUs write to __boot_cpu_mode with caches disabled, and thus a
> cached value of __boot_cpu_mode may be incoherent with that in memory.
> This could lead to a failure to detect mismatched boot modes.
> 
> This patch adds flushing to ensure that writes by secondaries to
> __boot_cpu_mode are made visible before we test against it.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Dave Martin <dave.martin@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Christoffer Dall <cdall@cs.columbia.edu>

Acked-by: Dave Martin <Dave.Martin@arm.com>

> ---
>  arch/arm/include/asm/virt.h | 12 ++++++++++++
>  arch/arm/kernel/setup.c     |  2 ++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/arch/arm/include/asm/virt.h b/arch/arm/include/asm/virt.h
> index 50af92b..4371f45 100644
> --- a/arch/arm/include/asm/virt.h
> +++ b/arch/arm/include/asm/virt.h
> @@ -29,6 +29,7 @@
>  #define BOOT_CPU_MODE_MISMATCH	PSR_N_BIT
>  
>  #ifndef __ASSEMBLY__
> +#include <asm/cacheflush.h>
>  
>  #ifdef CONFIG_ARM_VIRT_EXT
>  /*
> @@ -41,10 +42,21 @@
>   */
>  extern int __boot_cpu_mode;
>  
> +static inline void sync_boot_mode(void)
> +{
> +	/*
> +	 * As secondaries write to __boot_cpu_mode with caches disabled, we
> +	 * must flush the corresponding cache entries to ensure the visibility
> +	 * of their writes.
> +	 */
> +	sync_cache_r(&__boot_cpu_mode);
> +}
> +
>  void __hyp_set_vectors(unsigned long phys_vector_base);
>  unsigned long __hyp_get_vectors(void);
>  #else
>  #define __boot_cpu_mode	(SVC_MODE)
> +#define sync_boot_mode()
>  #endif
>  
>  #ifndef ZIMAGE
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index b4b1d39..4af9b38 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -744,6 +744,8 @@ static int __init meminfo_cmp(const void *_a, const void *_b)
>  void __init hyp_mode_check(void)
>  {
>  #ifdef CONFIG_ARM_VIRT_EXT
> +	sync_boot_mode();
> +
>  	if (is_hyp_mode_available()) {
>  		pr_info("CPU: All CPU(s) started in HYP mode.\n");
>  		pr_info("CPU: Virtualization extensions available.\n");
> -- 
> 1.8.1.1
> 
> 
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