linux-kernel - Re: [PATCH v4 12/21] KVM: selftests: Add a stage-2 MMU instance to kvm

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Message-ID: <3kuuj6toya5xlv74yrl4wg74b52wsvfqv3gigdbsdaqs7eibt5@th3b5x3dik7y>
Date: Fri, 2 Jan 2026 17:03:49 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oupton@...nel.org>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>, 
	Anup Patel <anup@...infault.org>, Paul Walmsley <pjw@...nel.org>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, 
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, loongarch@...ts.linux.dev, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 12/21] KVM: selftests: Add a stage-2 MMU instance to
 kvm_vm

On Tue, Dec 30, 2025 at 03:01:41PM -0800, Sean Christopherson wrote:
> Add a stage-2 MMU instance so that architectures that support nested
> virtualization (more specifically, nested stage-2 page tables) can create
> and track stage-2 page tables for running L2 guests.  Plumb the structure
> into common code to avoid cyclical dependencies, and to provide some line
> of sight to having common APIs for creating stage-2 mappings.
> 
> As a bonus, putting the member in common code justifies using stage2_mmu
> instead of tdp_mmu for x86.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Yosry Ahmed <yosry.ahmed@...ux.dev>

> ---
>  tools/testing/selftests/kvm/include/kvm_util.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index c1497515fa6a..371d55e0366e 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -116,7 +116,12 @@ struct kvm_vm {
>  	uint32_t dirty_ring_size;
>  	uint64_t gpa_tag_mask;
>  
> +	/*
> +	 * "mmu" is the guest's stage-1, with a short name because the vast
> +	 * majority of tests only care about the stage-1 MMU.
> +	 */
>  	struct kvm_mmu mmu;
> +	struct kvm_mmu stage2_mmu;
>  
>  	struct kvm_vm_arch arch;
>  
> -- 
> 2.52.0.351.gbe84eed79e-goog
>