linux-kernel - Re: [PATCH 0/1] KVM: arm64: Fix hyp VA size between layout and MMU

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Message-ID: <87qzscdlvi.wl-maz@kernel.org>
Date: Tue, 30 Dec 2025 15:34:25 +0000
From: Marc Zyngier <maz@...nel.org>
To: Petteri Kangaslampi <pekangas@...gle.com>
Cc: kvmarm@...ts.linux.dev,
	Oliver Upton <oliver.upton@...ux.dev>,
	Vincent Donnefort <vdonnefort@...gle.com>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/1] KVM: arm64: Fix hyp VA size between layout and MMU

On Tue, 23 Dec 2025 19:34:39 +0000,
Petteri Kangaslampi <pekangas@...gle.com> wrote:
> 
> All,
> 
> In the KVM initialization code, kvm_mmu_init() and
> kvm_compute_layout() use different logic when determining the
> hypervisor's virtual address space size. Specifically, the MMU code
> uses the larger of vabits_actual (the kernel's VA size) and
> IDMAP_VA_BITS (48 bits), while the VA layout code just uses the
> kernel's VA size.
> 
> This means that if the kernel is configured with a VA size of less
> than 48 bits (like happens in our environment), the assumptions used
> to calculate hyp_physvirt_offset and the code that determines VA
> ranges to use for mappings in hyp/nvhe/mm.c get out of sync, which can
> results in mapping failures.
> 
> The immediate fix is pretty obvious and attached here. This is against
> 6.12 but I don't think this code has changed recently. I think longer
> term refactoring knowledge of the hypervisor's address space into one
> place might be helpful; currently it is a bit spread out.

I'm sorry, but posting a patch against a kernel that is over a year
old doesn't help. It may apply, but it doesn't mean it works. Please
post a tested patch against the latest released kernel, or even
better, the latest -rc.

Thanks,

	M.

-- 
Jazz isn't dead. It just smells funny.