linux-kernel - Re: [PATCH v15 1/6] arm64/gcs: Ensure FGTs for EL1 GCS instructions are disabled

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Message-ID: <87ikihk4x3.wl-maz@kernel.org>
Date: Wed, 20 Aug 2025 23:24:24 +0100
From: Marc Zyngier <maz@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Shuah Khan <shuah@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 1/6] arm64/gcs: Ensure FGTs for EL1 GCS instructions are disabled

On Wed, 20 Aug 2025 15:14:41 +0100,
Mark Brown <broonie@...nel.org> wrote:
> 
> The initial EL2 setup for GCS did not include disabling of EL1 usage of
> GCS instructions, also disable these traps.  This is the first disabling
> of instruction traps, use x2 to store the value to be written.

Written where?

> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  arch/arm64/include/asm/el2_setup.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
> index 46033027510c..0ac14ea4dbc8 100644
> --- a/arch/arm64/include/asm/el2_setup.h
> +++ b/arch/arm64/include/asm/el2_setup.h
> @@ -355,6 +355,10 @@
>  
>  .Lskip_gce_fgt_\@:
>  
> +	orr	x2, x2, #HFGITR_EL2_nGCSEPP_MASK

What is x2 set to before this?

> +	orr	x2, x2, #HFGITR_EL2_nGCSSTR_EL1_MASK
> +	orr	x2, x2, #HFGITR_EL2_nGCSPUSHM_EL1_MASK
> +
>  .Lset_fgt_\@:
>  	msr_s	SYS_HFGRTR_EL2, x0
>  	msr_s	SYS_HFGWTR_EL2, x0

Followed by:

	msr_s	SYS_HFGITR_EL2, xzr

Puzzled.

	M.

-- 
Jazz isn't dead. It just smells funny.