[PATCH v1] arm: Support for the PXN CPU feature on ARMv7

[arnd@arndb.de (Arnd Bergmann)]

On Monday 24 November 2014 15:06:53 Catalin Marinas wrote:
> On Sat, Nov 22, 2014 at 10:42:36AM +0000, Jungseung Lee wrote:
> > diff --git a/arch/arm/include/asm/pgalloc.h b/arch/arm/include/asm/pgalloc.h

> In general we put the #ifdef outside the function:
> 
> #if __LINUX_ARM_ARCH__ >= 7 && !defined(CONFIG_ARM_LPAE)
> static inline bool cpu_has_classic_pxn(void)
> {
> 	unsigned int vmsa = (read_cpuid_ext(CPUID_EXT_MMFR0) & 0xf) >> 0;
> 	return vmsa == 4;
> }
> #else
> static inline bool cpu_has_classic_pxn(void)
> {
> 	return false;
> }
> #endif
> 
> I used __LINUX_ARM_ARCH__ instead of CONFIG_CPU_V7 to cope with kernel
> images built for both v6 and v7. You could also check for
> cpu_architecture() >= 7, though with a bit of performance impact.

Regarding the style, I think the best way to express it is

	if (__LINUX_ARM_ARCH__ >= 7 && !IS_ENABLED(CONFIG_ARM_LPAE) && (vmsa == 4))
		return true;
	return false;

This way you can avoid the #ifdef and still get the compile-time
optimization.

Checking for (__LINUX_ARM_ARCH__ >= 6 && cpu_architecture >= 7) would
also make it work for a combined armv6/v7 kernel.

	Arnd