Re: [PATCH v7 11/23] KVM: arm64: Share arm64 code with s390

[Marc Zyngier <maz@kernel.org>]

On Mon, 31 Aug 2026 15:47:48 +0100,
Steffen Eiden <seiden@linux.ibm.com> wrote:
> 
> Mark functions that s390 can use to implement arm on s390 as shared
> functions.
> 
> No functional change.
> 
> Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
> ---
>  arch/arm64/kvm/arm.c         | 3 +++
>  arch/arm64/kvm/guest.c       | 6 ++++++
>  arch/arm64/kvm/handle_exit.c | 6 ++++++
>  arch/arm64/kvm/mmio.c        | 2 ++
>  4 files changed, 17 insertions(+)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 8b080804bc90..6b92a3c1d490 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1603,6 +1603,7 @@ static unsigned long system_supported_vcpu_features(void)
>  	return features;
>  }
>  
> +#ifdef ARM64_S390_COMMON
>  static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
>  					const struct kvm_vcpu_init *init)
>  {
> @@ -1656,6 +1657,8 @@ static bool kvm_vcpu_init_changed(struct kvm_vcpu *vcpu,
>  			     KVM_VCPU_MAX_FEATURES);
>  }
>  
> +#endif /* ARM64_S390_COMMON */
> +
>  static int kvm_setup_vcpu(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm *kvm = vcpu->kvm;
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 773f6c8e5026..6ca5a9f357cd 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -62,6 +62,7 @@ const struct kvm_stats_header kvm_vcpu_stats_header = {
>  		       sizeof(kvm_vcpu_stats_desc),
>  };
>  
> +#ifdef ARM64_S390_COMMON
>  static bool core_reg_offset_is_vreg(u64 off)
>  {
>  	return off >= KVM_REG_ARM_CORE_REG(fp_regs.vregs) &&
> @@ -306,6 +307,8 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  	return err;
>  }
>  
> +#endif /* ARM64_S390_COMMON */
> +
>  #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)
>  #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
>  #define vq_present(vqs, vq) (!!((vqs)[vq_word(vq)] & vq_mask(vq)))
> @@ -543,6 +546,7 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
>  	return -EINVAL;
>  }
>  
> +#ifdef ARM64_S390_COMMON
>  static int copy_core_reg_indices(const struct kvm_vcpu *vcpu,
>  				 u64 __user *uindices)
>  {
> @@ -591,6 +595,8 @@ static unsigned long num_core_regs(const struct kvm_vcpu *vcpu)
>  	return copy_core_reg_indices(vcpu, NULL);
>  }
>  
> +#endif /* ARM64_S390_COMMON */
> +
>  static unsigned long num_sve_regs(const struct kvm_vcpu *vcpu)
>  {
>  	const unsigned int slices = vcpu_sve_slices(vcpu);
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index db37678dcb05..6e59a7b12d40 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -213,6 +213,7 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu)
>  	return 0;
>  }
>  
> +#ifdef ARM64_S390_COMMON
>  static int kvm_handle_unknown_ec(struct kvm_vcpu *vcpu)
>  {
>  	u64 esr = kvm_vcpu_get_esr(vcpu);
> @@ -224,6 +225,8 @@ static int kvm_handle_unknown_ec(struct kvm_vcpu *vcpu)
>  	return 1;
>  }
>  
> +#endif /* ARM64_S390_COMMON */
> +
>  /*
>   * Guest access to SVE registers should be routed to this handler only
>   * when the system doesn't support SVE.
> @@ -404,6 +407,7 @@ static exit_handle_fn arm_exit_handlers[] = {
>  	[ESR_ELx_EC_GCS]	= kvm_handle_gcs,
>  };
>  
> +#ifdef ARM64_S390_COMMON
>  static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
>  {
>  	u64 esr = kvm_vcpu_get_esr(vcpu);
> @@ -439,6 +443,8 @@ static int handle_trap_exceptions(struct kvm_vcpu *vcpu)
>  	return handled;
>  }
>  
> +#endif /* ARM64_S390_COMMON */

Why the exit handler, and not the EC handlers aside from the UNKNOWN
one? Yes, you probably aren't there yet in this series, but I can tell
you are going to add more and more of these.

But the EC array is absolutely architectural, and there is no good
reason to maintain your own.

So instead of this, why not keep the EC array altogether, and
implement stubs for the ECs you don't support?

	M.

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