Re: [PATCH v6 09/33] arm64: Prepare sharing arm64 headers with s390

[Marc Zyngier <maz@kernel.org>]

On Wed, 12 Aug 2026 16:36:05 +0100,
Steffen Eiden <seiden@linux.ibm.com> wrote:

[...]

> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 46c8d7928b3f..22770c1132cb 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -56,6 +56,36 @@
>  #define KVM_REQ_MAP_L1_VNCR_EL2		KVM_ARCH_REQ(10)
>  #define KVM_REQ_VGIC_PROCESS_UPDATE	KVM_ARCH_REQ(11)
>  
> +/*
> + * If we encounter a data abort without valid instruction syndrome
> + * information, report this to user space.  User space can (and
> + * should) opt in to this feature if KVM_CAP_ARM_NISV_TO_USER is
> + * supported.
> + */
> +#define KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER	0
> +/* Memory Tagging Extension enabled for the guest */
> +#define KVM_ARCH_FLAG_MTE_ENABLED			1
> +/* At least one vCPU has ran in the VM */
> +#define KVM_ARCH_FLAG_HAS_RAN_ONCE			2
> +/* The vCPU feature set for the VM is configured */
> +#define KVM_ARCH_FLAG_VCPU_FEATURES_CONFIGURED		3
> +/* PSCI SYSTEM_SUSPEND enabled for the guest */
> +#define KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED		4
> +/* VM counter offset */
> +#define KVM_ARCH_FLAG_VM_COUNTER_OFFSET			5
> +/* Timer PPIs made immutable */
> +#define KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE		6
> +/* Initial ID reg values loaded */
> +#define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		7
> +/* Fine-Grained UNDEF initialised */
> +#define KVM_ARCH_FLAG_FGU_INITIALIZED			8
> +/* SVE exposed to guest */
> +#define KVM_ARCH_FLAG_GUEST_HAS_SVE			9
> +/* MIDR_EL1, REVIDR_EL1, and AIDR_EL1 are writable from userspace */
> +#define KVM_ARCH_FLAG_WRITABLE_IMP_ID_REGS		10
> +/* Unhandled SEAs are taken to userspace */
> +#define KVM_ARCH_FLAG_EXIT_SEA				11
> +

I don't mind the move, but please add a comment indicating that these
are bit indices for for kvm_arch::flags, as we have now lost locality.

And whilst we're at it, there is not reason why this has to be a set
of #define, it can perfectly be an enum, as the numbers themselves
have no particular meaning. Something like the untested hack below.

	M.

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 08b2f24dc3c79..402bbb5eb0d91 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -306,6 +306,39 @@ enum fgt_group_id {
 	__NR_FGT_GROUP_IDS__
 };
 
+/* Bit indices for kvm_arch::flags */
+enum kvm_arch_flag_bits {
+	/*
+	 * If we encounter a data abort without valid instruction syndrome
+	 * information, report this to user space.  User space can (and
+	 * should) opt in to this feature if KVM_CAP_ARM_NISV_TO_USER is
+	 * supported.
+	 */
+	KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
+	/* Memory Tagging Extension enabled for the guest */
+	KVM_ARCH_FLAG_MTE_ENABLED,
+	/* At least one vCPU has ran in the VM */
+	KVM_ARCH_FLAG_HAS_RAN_ONCE,
+	/* The vCPU feature set for the VM is configured */
+	KVM_ARCH_FLAG_VCPU_FEATURES_CONFIGURED,
+	/* PSCI SYSTEM_SUSPEND enabled for the guest */
+	KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED,
+	/* VM counter offset */
+	KVM_ARCH_FLAG_VM_COUNTER_OFFSET,
+	/* Timer PPIs made immutable */
+	KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE,
+	/* Initial ID reg values loaded */
+	KVM_ARCH_FLAG_ID_REGS_INITIALIZED,
+	/* Fine-Grained UNDEF initialised */
+	KVM_ARCH_FLAG_FGU_INITIALIZED,
+	/* SVE exposed to guest */
+	KVM_ARCH_FLAG_GUEST_HAS_SVE,
+	/* MIDR_EL1, REVIDR_EL1, and AIDR_EL1 are writable from userspace */
+	KVM_ARCH_FLAG_WRITABLE_IMP_ID_REGS,
+	/* Unhandled SEAs are taken to userspace */
+	KVM_ARCH_FLAG_EXIT_SEA,
+};
+
 struct kvm_arch {
 	struct kvm_s2_mmu mmu;
 
@@ -338,35 +371,7 @@ struct kvm_arch {
 	/* Protects VM-scoped configuration data */
 	struct mutex config_lock;
 
-	/*
-	 * If we encounter a data abort without valid instruction syndrome
-	 * information, report this to user space.  User space can (and
-	 * should) opt in to this feature if KVM_CAP_ARM_NISV_TO_USER is
-	 * supported.
-	 */
-#define KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER	0
-	/* Memory Tagging Extension enabled for the guest */
-#define KVM_ARCH_FLAG_MTE_ENABLED			1
-	/* At least one vCPU has ran in the VM */
-#define KVM_ARCH_FLAG_HAS_RAN_ONCE			2
-	/* The vCPU feature set for the VM is configured */
-#define KVM_ARCH_FLAG_VCPU_FEATURES_CONFIGURED		3
-	/* PSCI SYSTEM_SUSPEND enabled for the guest */
-#define KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED		4
-	/* VM counter offset */
-#define KVM_ARCH_FLAG_VM_COUNTER_OFFSET			5
-	/* Timer PPIs made immutable */
-#define KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE		6
-	/* Initial ID reg values loaded */
-#define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		7
-	/* Fine-Grained UNDEF initialised */
-#define KVM_ARCH_FLAG_FGU_INITIALIZED			8
-	/* SVE exposed to guest */
-#define KVM_ARCH_FLAG_GUEST_HAS_SVE			9
-	/* MIDR_EL1, REVIDR_EL1, and AIDR_EL1 are writable from userspace */
-#define KVM_ARCH_FLAG_WRITABLE_IMP_ID_REGS		10
-	/* Unhandled SEAs are taken to userspace */
-#define KVM_ARCH_FLAG_EXIT_SEA				11
+	/* VM-wide flags, described in kvm_arch_flag_bits */
 	unsigned long flags;
 
 	/* VM-wide vCPU feature set */

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