linux-kernel - Re: [PATCH v4 2/3] arm64: Add missing

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Message-ID: <86jzrin8nq.wl-maz@kernel.org>
Date:   Thu, 19 Oct 2023 12:39:21 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Miguel Luis <miguel.luis@...cle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Eric Auger <eric.auger@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.linux.dev
Subject: Re: [PATCH v4 2/3] arm64: Add missing _EL2 encodings

On Mon, 16 Oct 2023 12:17:41 +0100,
Miguel Luis <miguel.luis@...cle.com> wrote:
> 
> Some _EL2 encodings are missing. Add them.
> 
> Signed-off-by: Miguel Luis <miguel.luis@...cle.com>
> ---
>  arch/arm64/include/asm/sysreg.h | 39 +++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index ba5db50effec..8653fb67a339 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h

[...]

> +#define SYS_SDER32_EL2			sys_reg(3, 4, 1, 3, 1)

[...]

> +#define SYS_VSTTBR_EL2			sys_reg(3, 4, 2, 6, 0)
> +#define SYS_VSTCR_EL2			sys_reg(3, 4, 2, 6, 2)

[...]

> +#define SYS_CNTHVS_TVAL_EL2		sys_reg(3, 4, 14, 4, 0)
> +#define SYS_CNTHVS_CTL_EL2		sys_reg(3, 4, 14, 4, 1)
> +#define SYS_CNTHVS_CVAL_EL2		sys_reg(3, 4, 14, 4, 2)
> +#define SYS_CNTHPS_TVAL_EL2		sys_reg(3, 4, 14, 5, 0)
> +#define SYS_CNTHPS_CTL_EL2		sys_reg(3, 4, 14, 5, 1)
> +#define SYS_CNTHPS_CVAL_EL2		sys_reg(3, 4, 14, 5, 2)

While the secure definitions seem correct, what is the rationale
behind their presence here? They cannot be trapped from non-secure,
and the pseudocode is pretty explicit:

	if !IsCurrentSecurityState(SS_Secure) then
		UNDEFINED;

Given that, they cannot be trapped, handled or accessed from a KVM
guest, as Linux on arm64 *always* runs non-secure.

	M.

-- 
Without deviation from the norm, progress is not possible.