Re: [PATCH v2 1/3] KVM: s390: Toggle operation exception for userspace

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 07.05.26 um 22:08 schrieb Eric Farman:
> The KVM_CAP_S390_USER_OPEREXEC capability allows operation exceptions
> to be forwarded to userspace. But the actual enablement at the hardware
> level occurs in kvm_arch_vcpu_postcreate(), and only if STFLE.74 or
> user_instr0 are enabled. The latter is associated with a separate
> capability (KVM_CAP_S390_USER_INSTR0), so the only way this happens
> for the USER_OPEREXEC capability is if STFLE.74 is enabled. KVM
> unconditionally enables this bit in kvm_arch_init_vm(), but the guest
> could disable it from the CPU model and thus ignore this capability.
> 
> Add USER_OPEREXEC to the check in kvm_arch_vcpu_postcreate(), such that
> either capability would enable this type of exception.
> 
> Fixes: 8e8678e740ec ("KVM: s390: Add capability that forwards operation exceptions")
> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>

Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>


> ---
>   arch/s390/kvm/kvm-s390.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index e09960c2e6ed..a91a42174302 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -3521,7 +3521,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
>   		vcpu->arch.gmap = vcpu->kvm->arch.gmap;
>   		sca_add_vcpu(vcpu);
>   	}
> -	if (test_kvm_facility(vcpu->kvm, 74) || vcpu->kvm->arch.user_instr0)
> +	if (test_kvm_facility(vcpu->kvm, 74) || vcpu->kvm->arch.user_instr0 ||
> +	    vcpu->kvm->arch.user_operexec)
>   		vcpu->arch.sie_block->ictl |= ICTL_OPEREXC;
>   }
>