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Subject: Re: [PATCH v2 1/2] KVM: Refactor kvm_arch_vcpu_fault() to return a
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To:     David Hildenbrand <david@redhat.com>,
        Hou Wenlong <houwenlong93@linux.alibaba.com>,
        kvm@vger.kernel.org
Cc:     Sean Christopherson <seanjc@google.com>,
        Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Paul Mackerras <paulus@ozlabs.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
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        linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
        kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-s390@vger.kernel.org
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <d29447d4-a1b4-7f12-7bbc-8dc24cb38b72@redhat.com>
Date:   Thu, 12 Aug 2021 17:41:22 +0200
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On 12/08/21 11:04, David Hildenbrand wrote:
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> 
> But at the same time I wonder if we should just get rid of 
> CONFIG_KVM_S390_UCONTROL and consequently kvm_arch_vcpu_fault().
> 
> In practice CONFIG_KVM_S390_UCONTROL, is never enabled in any reasonable 
> kernel build and consequently it's never tested; further, exposing the 
> sie_block to user space allows user space to generate random SIE 
> validity intercepts.
> 
> CONFIG_KVM_S390_UCONTROL feels like something that should just be 
> maintained out of tree by someone who really needs to hack deep into hw 
> virtualization for testing purposes etc.

I have no preference either way.  It should definitely have selftests, 
but in x86 land there are some features that are not covered by QEMU and 
were nevertheless accepted upstream with selftests.

Paolo