Re: [PATCH v4 2/3] arm64: Add missing _EL2 encodings

From: Miguel Luis <miguel.luis@oracle.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Jing Zhang <jingzhangos@google.com>,
	Eric Auger <eric.auger@redhat.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvmarm@lists.linux.dev" <kvmarm@lists.linux.dev>
Subject: Re: [PATCH v4 2/3] arm64: Add missing _EL2 encodings
Date: Thu, 19 Oct 2023 13:23:09 +0000	[thread overview]
Message-ID: <21F82E44-6D93-4F4C-8991-F14948673F54@oracle.com> (raw)
In-Reply-To: <86jzrin8nq.wl-maz@kernel.org>

Hi Marc,

> On 19 Oct 2023, at 11:39, Marc Zyngier <maz@kernel.org> wrote:
> 
> On Mon, 16 Oct 2023 12:17:41 +0100,
> Miguel Luis <miguel.luis@oracle.com> wrote:
>> 
>> Some _EL2 encodings are missing. Add them.
>> 
>> Signed-off-by: Miguel Luis <miguel.luis@oracle.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.
> 

Thank you for clarifying.

Those definitions were needed for the refinement on patch 3 which clearly
didn’t considered that statement beforehand.

Yet, should we keep them here so they could be used?

Thank you
Miguel

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