Date: Thu, 13 Aug 2026 14:50:48 +0100
Message-ID: <864igy164n.wl-maz@kernel.org>
From: Marc Zyngier <maz@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: kvmarm@lists.linux.dev,
	linux-arm-kernel@lists.infradead.org,
	Oliver Upton <oupton@kernel.org>
Subject: Re: [PATCH] KVM: arm64: Avoid mismatched accesses to 'struct kvm_nvhe_init_params'
In-Reply-To: <20260813131717.5885-1-will@kernel.org>
References: <20260813131717.5885-1-will@kernel.org>
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On Thu, 13 Aug 2026 14:17:16 +0100,
Will Deacon <will@kernel.org> wrote:
> 
> When running with hVHE enabled, ___kvm_hyp_init() calls
> __kvm_init_el2_state() on the CPU initialisation path during onlining
> and resume from suspend.
> 
> In order to avoid clobbering the link register across this call, it is
> stashed away in the 'tmp' member of 'struct kvm_nvhe_init_params',
> however this save/restore operation is performed with the stage-1 MMU
> disabled at EL2 and therefore gives rise to coherency problems because
> the field is not aligned or padded to the CWG. For example, a cacheable
> write to a physically-adjacent structure sharing the same cacheline
> could lead to an eviction and subsequent write-back, overwriting the
> saved LR while the incoming CPU is executing __kvm_init_el2_state().
> 
> Save the lr in far_el2 and remove the 'tmp' member from
> 'struct kvm_nvhe_init_params' altogether.
> 
> Cc: Oliver Upton <oupton@kernel.org>
> Cc: Marc Zyngier <maz@kernel.org>
> Fixes: afa9b48f327c ("KVM: arm64: Shave a few bytes from the EL2 idmap code")
> Signed-off-by: Will Deacon <will@kernel.org>

Oh hum... That's a nice one. Thanks for getting to the bottom of it.

FWIW:

Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org

	M.

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