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Date: Mon, 22 Jun 2026 17:20:11 -0700
From: Oliver Upton <oupton@kernel.org>
To: Fuad Tabba <fuad.tabba@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>, Joey Gouly <joey.gouly@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Steffen Eiden <seiden@linux.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Shuah Khan <shuah@kernel.org>,
	Christoffer Dall <christoffer.dall@linaro.org>,
	Victor Kamensky <victor.kamensky@linaro.org>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] KVM: arm64: Fix and test MMIO sign-extending loads
Message-ID: <ajnRO9oMrVCXQT9t@kernel.org>
References: <20260622190701.2039766-1-fuad.tabba@linux.dev>
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In-Reply-To: <20260622190701.2039766-1-fuad.tabba@linux.dev>

On Mon, Jun 22, 2026 at 08:06:59PM +0100, Fuad Tabba wrote:
> Hi folks,
> 
> A sign-extending load (LDRSB/LDRSH/LDRSW) from emulated MMIO returns a
> zero-extended value rather than the sign-extended one the architecture
> requires; vcpu_data_host_to_guest() strips the sign bits when it masks
> the data to the access width.
> 
> If my git archeology is right, the masking dates to 2014 (b30070862edbd,
> big-endian support) and has been wrong ever since, but sign-extending
> loads from device memory are rare enough that nobody hit it. Patch 1
> fixes it; patch 2 adds a selftest so it doesn't regress.
> 
> Cheers,
> /fuad
> 
> Fuad Tabba (2):
>   KVM: arm64: Fix sign-extension of MMIO loads
>   KVM: arm64: selftests: Add MMIO sign-extending load test

For the oddball guest :)

Reviewed-by: Oliver Upton <oupton@kernel.org>

Thanks,
Oliver