[PATCH v2 2/4] ARM: nommu: dynamic exception base address setting

[Vladimir Murzin]

On 08/03/17 03:21, Greg Ungerer wrote:
> 
> Hi Afzal,
> 
> On 21/01/17 19:20, afzal mohammed write:
>> No-MMU dynamic exception base address configuration on CP15
>> processors. In the case of low vectors, decision based on whether
>> security extensions are enabled & whether remap vectors to RAM
>> CONFIG option is selected.
>>
>> For no-MMU without CP15, current default value of 0x0 is retained.
>>
>> Signed-off-by: afzal mohammed <afzal.mohd.ma at gmail.com>
> 
> This patch (which is in mainline now as commit f8300a0b5d) breaks
> my patch series to support running the Versatile QEMU target with
> a nommu configured linux kernel. This series can be found here:
> 
>  http://lists.infradead.org/pipermail/linux-arm-kernel/2017-February/490653.html
> 
> The problem is that QEMU is failing out with:
> 
>  qemu: fatal: Trying to execute code outside RAM or ROM at 0x41069264
> 
> when this your patch is applied.
> 
> 
>> diff --git a/arch/arm/mm/nommu.c b/arch/arm/mm/nommu.c
>> index 2740967727e2..20ac52579952 100644
>> --- a/arch/arm/mm/nommu.c
>> +++ b/arch/arm/mm/nommu.c
>> @@ -11,6 +11,7 @@
>>  #include <linux/kernel.h>
>>  
>>  #include <asm/cacheflush.h>
>> +#include <asm/cp15.h>
>>  #include <asm/sections.h>
>>  #include <asm/page.h>
>>  #include <asm/setup.h>
>> @@ -22,6 +23,8 @@
>>  
>>  #include "mm.h"
>>  
>> +unsigned long vectors_base;
>> +
>>  #ifdef CONFIG_ARM_MPU
>>  struct mpu_rgn_info mpu_rgn_info;
>>  
>> @@ -278,15 +281,60 @@ static void sanity_check_meminfo_mpu(void) {}
>>  static void __init mpu_setup(void) {}
>>  #endif /* CONFIG_ARM_MPU */
>>  
>> +#ifdef CONFIG_CPU_CP15
>> +#ifdef CONFIG_CPU_HIGH_VECTOR
>> +static unsigned long __init setup_vectors_base(void)
>> +{
>> +	unsigned long reg = get_cr();
>> +
>> +	set_cr(reg | CR_V);
>> +	return 0xffff0000;
>> +}
>> +#else /* CONFIG_CPU_HIGH_VECTOR */
>> +/* Write exception base address to VBAR */
>> +static inline void set_vbar(unsigned long val)
>> +{
>> +	asm("mcr p15, 0, %0, c12, c0, 0" : : "r" (val) : "cc");
>> +}
>> +
>> +/*
>> + * Security extensions, bits[7:4], permitted values,
>> + * 0b0000 - not implemented, 0b0001/0b0010 - implemented
>> + */
>> +static inline bool security_extensions_enabled(void)
>> +{
>> +	return !!cpuid_feature_extract(CPUID_EXT_PFR1, 4);
> 
> The problem is here. This ends up generating the asm code:
> 
>   2ebacc:       ee103f31        mrc     15, 0, r3, cr0, cr1, {1}
> 
> QEMU loses it on running this (confirmed by single stepping here).
> 
> Is this valid for an ARM926EJ?
> Or is it QEMU that is at fault here...
> 
> I can see that this would be valid for an ARM11 for example
> (http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0360f/CHDGIJFB.html)
> 
> But I could not see that it is valid on an ARM926
> (http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0198e/I1003211.html)
> 
> Maybe I am looking in the wrong place though.
> 
> Thoughts?

I'm wondering if something like bellow would help?

diff --git a/arch/arm/mm/nommu.c b/arch/arm/mm/nommu.c
index 3b5c7aa..25542ec 100644
--- a/arch/arm/mm/nommu.c
+++ b/arch/arm/mm/nommu.c
@@ -303,7 +303,11 @@ static inline void set_vbar(unsigned long val)
  */
 static inline bool security_extensions_enabled(void)
 {
+#if __LINUX_ARM_ARCH__ < 6
+	return 0;
+#else
 	return !!cpuid_feature_extract(CPUID_EXT_PFR1, 4);
+#endif
 }
 
 static unsigned long __init setup_vectors_base(void)

Cheers
Vladimir

> 
> Regards
> Greg
> 
>