linux-kernel - Re: [PATCH v2 2/6] arm64: trap to EL1 accesses to AMU counters from EL0

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Message-ID: <20200123173456.GA20475@arm.com>
Date:   Thu, 23 Jan 2020 17:34:56 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     catalin.marinas@....com, will@...nel.org, mark.rutland@....com,
        maz@...nel.org, suzuki.poulose@....com, sudeep.holla@....com,
        dietmar.eggemann@....com, peterz@...radead.org, mingo@...hat.com,
        ggherdovich@...e.cz, vincent.guittot@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Steve Capper <steve.capper@....com>
Subject: Re: [PATCH v2 2/6] arm64: trap to EL1 accesses to AMU counters from
 EL0

On Thursday 23 Jan 2020 at 17:04:32 (+0000), Valentin Schneider wrote:
> On 18/12/2019 18:26, Ionela Voinescu wrote:
> > +/*
> > + * reset_amuserenr_el0 - reset AMUSERENR_EL0 if AMUv1 present
> > + */
> > +	.macro	reset_amuserenr_el0, tmpreg
> > +	mrs	\tmpreg, id_aa64pfr0_el1	// Check ID_AA64PFR0_EL1
> > +	ubfx	\tmpreg, \tmpreg, #ID_AA64PFR0_AMU_SHIFT, #4
> > +	cbz	\tmpreg, 9000f			// Skip if no AMU present
> > +	msr_s	SYS_AMUSERENR_EL0, xzr		// Disable AMU access from EL0
> > +9000:
> 
> AIUI you can steer away from the obscure numbering scheme and define the
> label using the macro counter:
> 
> 	cbz \tmpreg, .Lskip_\@
> 	[...]
> .Lskip_\@:
> 	.endm
> 

Cool, good to know! Although calling it "obscure numbering scheme" does
make it more appealing to use.

Thanks, I'll change it in the next version :).

Ionela.

> 
> > +	.endm