Re: [PATCH v17 06/20] KVM: arm64: CCA: Add a new mode for supporting Realm guests

On Wed, 09 Sep 2026 04:26:41 +0100,
Kohei Enju [off-list ref] wrote:

Hi Suzuki,

On 09/08 17:22, Suzuki K Poulose wrote:

quoted

Add an explicit mode to support Arm CCA guests.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 arch/arm64/include/asm/kvm_host.h               | 1 +
 arch/arm64/kvm/arm.c                            | 5 +++++
 3 files changed, 9 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 68647ff4bdd24..1afe3df3b923e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt

@@ -3256,6 +3256,9 @@ Kernel parameters
 			nested: VHE-based mode with support for nested
 				virtualization. Requires at least ARMv8.4
 				hardware (with FEAT_NV2).
+			rmm: Support for running confidential guests in Realm
+			     world using RMM, as defined by Arm Confidential
+			     Compute Architecture (CCA)
 
 			Defaults to VHE/nVHE based on hardware support. Setting
 			mode to "protected" will disable kexec and hibernation

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index b2e99c5cb1cd3..31ae9d8d8e92f 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h

@@ -69,6 +69,7 @@ enum kvm_mode {
 	KVM_MODE_DEFAULT,
 	KVM_MODE_PROTECTED,
 	KVM_MODE_NV,
+	KVM_MODE_RMM,
 	KVM_MODE_NONE,
 };
 #ifdef CONFIG_KVM

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 9af3bbb2f8c24..50f0adfadab38 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c

@@ -3264,6 +3264,11 @@ static int __init early_kvm_mode_cfg(char *arg)
 		return 0;
 	}
 
+	if (strcmp(arg, "rmm") == 0 && !WARN_ON(!is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_RMM;
+		return 0;
+	}

Does this make NV support and CCA Realm VM support mutually exclusive?

Until the v16 series, we could run Realm VMs with:
  'kvm-arm.mode=nested'

As far as the AArch64 architecture is concerned, there does not seem to
be a reason to make them mutually exclusive. I am therefore wondering
whether this restriction is intentional.

I have a hack somewhere that will allow this, but this requires to
change the above to be a capability mask rather than a simple
enumeration. I'll see if I can spin that as a separate series.

	M.

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