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Subject: Re: [PATCH v2 08/23] arm64: cpufeature: Store every ID register with
 its overrides applied
To: Fuad Tabba <fuad.tabba@linux.dev>
Cc: Will Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.org,
 linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@kernel.org>,
 =?UTF-8?Q?=C8=98tefania_Ion?= <stefion@google.com>,
 Catalin Marinas <catalin.marinas@arm.com>,
 Pankaj Patil <pankaj.patil@oss.qualcomm.com>, Borislav Petkov
 <bp@alien8.de>, Lorenzo Pieralisi <lpieralisi@kernel.org>,
 Jinjie Ruan <ruanjinjie@huawei.com>, Mark Rutland <mark.rutland@arm.com>,
 Tarun Sahu <tarunsahu@google.com>, David Woodhouse <dwmw@amazon.co.uk>,
 Peter Zijlstra <peterz@infradead.org>, Marc Zyngier <maz@kernel.org>
References: <20261009100738.31288-1-will@kernel.org>
 <20261009100738.31288-9-will@kernel.org>
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From: Ben Horgan <ben.horgan@arm.com>
In-Reply-To: <CA+EHjTwgfGzS92thiGFcJ1NgoA732RBqv3gJUWF1gJAE-jANFA@mail.gmail.com>
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Hi Fuad,

On 11/10/2026 08:34, Fuad Tabba wrote:
> Hi Ben,
> 
> On Fri, 09 Oct 2026 16:51:14 +0100, Ben Horgan <ben.horgan@arm.com> wrote:
> [...]
>>> the same way. Everything read with read_cpuid() goes through
>>> read_cpuid_with_overrides(). CTR_EL0 and CNTFRQ_EL0, which are read
> [...]
>> For completeness shouldn't read_cpuid(SMIDR_EL1) change to
>> read_cpuid_with_overrides(SMIDR_EL1)?
> 
> "Everything" should have said every register in arm64_ftr_regs[], and
> SMIDR_EL1 isn't one of them, so read_cpuid_with_overrides() would hit
> the WARN_ON() in get_arm64_ftr_reg() whenever SME is enabled.

Thanks for the explanation. If I understand correctly, SMIDR_EL1 isn't in arm64_ftr_regs[] because
there is no need to sanitize SMIDR_EL1 to give a consistent view across cpus. If and when support
for sme priority is added then a unified view of the SMIDR_EL1.HIP, highest implement priority,
would be needed and so at that point deserve a place in arm64_ftr_regs[].

Cheers,
Ben

> 
> Thanks,
> /fuad