linux-kernel - Re: [PATCH 01/13] arm/arm64: Add new is_kernel_in_hyp

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Message-ID: <559E476E.2000306@arm.com>
Date:	Thu, 09 Jul 2015 11:05:34 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH 01/13] arm/arm64: Add new is_kernel_in_hyp_mode predicate

On 09/07/15 10:42, Mark Rutland wrote:
> Hi,
> 
>> +static inline bool is_kernel_in_hyp_mode(void)
>> +{
>> +	u64 el;
>> +
>> +	asm("mrs %0, CurrentEL" : "=r" (el));
>> +	return el == CurrentEL_EL2;
>> +}
> 
> If you can include cputype.h, I think this can be:
> 
> static inline bool is_kernel_in_hyp_mode(void)
> {
> 	return read_cpuid(CurrentEL) == CurrentEL_EL2;
> }

This would indeed work, but CurrentEL is hardly an ID register. I feel
slightly uncomfortable using read_cpuid (which might return a cached
version at some point) for random system registers.

Thoughts?

	M.
-- 
Jazz is not dead. It just smells funny...
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