linux-kernel - Re: [PATCH v11 9/9] arm64: armv8_deprecated: apply FEAT

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Message-ID: <aQ4WzxQl+aVJcBaL@e129823.arm.com>
Date: Fri, 7 Nov 2025 15:57:03 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>, miko.lenczewski@....com,
	Kevin Brodsky <kevin.brodsky@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>, yangyicong@...ilicon.com,
	scott@...amperecomputing.com, Joey Gouly <joey.gouly@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Paolo Bonzini <pbonzini@...hat.com>, shuah <shuah@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v11 9/9] arm64: armv8_deprecated: apply FEAT_LSUI for
 swpX emulation.

Hi Arnd,

> >> > apply FEAT_LSUI instruction to emulate deprecated swpX instruction.
> >>
> >> Can you explain in the changrelog why you do this?
> >>
> >> In particular, is this a performance optimization or is this required
> >> for correctness in some scenario?
> >
> > I think the main purpose using for this is to "remove the toggling the
> > PSTATE.PAN" bit. so that remove some *potential* problem which can
> > happen when PAN bit is cleared.
>
> Ok, I see. This should definitely be part of the commit
> log for the patch in addition to the cover letter.

Thanks. I'll add detail in next spin after receving other comments.

[...]

--
Sincerely,
Yeoreum Yun