From: "Arnd Bergmann" <arnd@arndb.de>
To: "Yeoreum Yun" <yeoreum.yun@arm.com>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will@kernel.org>, "Marc Zyngier" <maz@kernel.org>,
"Mark Brown" <broonie@kernel.org>,
"Oliver Upton" <oliver.upton@linux.dev>,
miko.lenczewski@arm.com, "Kevin Brodsky" <kevin.brodsky@arm.com>,
"Ard Biesheuvel" <ardb@kernel.org>,
"Suzuki K Poulose" <suzuki.poulose@arm.com>,
"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
yangyicong@hisilicon.com, scott@os.amperecomputing.com,
"Joey Gouly" <joey.gouly@arm.com>,
"Zenghui Yu" <yuzenghui@huawei.com>,
"Paolo Bonzini" <pbonzini@redhat.com>, shuah <shuah@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev,
kvm@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v11 9/9] arm64: armv8_deprecated: apply FEAT_LSUI for swpX emulation.
Date: Fri, 07 Nov 2025 15:24:12 +0100 [thread overview]
Message-ID: <a9f4eb49-b06e-4941-a75a-df39f5d3d735@app.fastmail.com> (raw)
In-Reply-To: <aQ3/35146HkAqM+I@e129823.arm.com>
On Fri, Nov 7, 2025, at 15:19, Yeoreum Yun wrote:
>> On Thu, Nov 6, 2025, at 10:40, Yeoreum Yun wrote:
>> > 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.
> also, though swpb might add some complexity, but swp can get
> a little bit of benifit by removing the ll/sc way and reduce
> the amount of instructions.
This part I think you can ignore in the patch description,
unless there is an additional problem with possibly mixing ll/sc
and lse atomics that you are trying to solve.
Arnd
next prev parent reply other threads:[~2025-11-07 14:24 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-06 9:40 [PATCH v11 0/9] support FEAT_LSUI Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 1/9] arm64: cpufeature: add FEAT_LSUI Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 2/9] KVM: arm64: expose FEAT_LSUI to guest Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 3/9] KVM: arm64: kselftest: set_id_regs: add test for FEAT_LSUI Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 4/9] arm64: Kconfig: Detect toolchain support for LSUI Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 5/9] arm64: futex: refactor futex atomic operation Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 6/9] arm64: futex: support futex with FEAT_LSUI Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 7/9] arm64: separate common LSUI definitions into lsui.h Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 8/9] arm64: armv8_deprecated: convert user_swpX to inline function Yeoreum Yun
2025-11-06 9:40 ` [PATCH v11 9/9] arm64: armv8_deprecated: apply FEAT_LSUI for swpX emulation Yeoreum Yun
2025-11-07 11:52 ` Arnd Bergmann
2025-11-07 14:19 ` Yeoreum Yun
2025-11-07 14:24 ` Arnd Bergmann [this message]
2025-11-07 15:57 ` Yeoreum Yun
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