linux-kernel - Re: [RFC PATCH 3/3] KVM: x86: Use KVM_BUG/KVM_BUG_ON to handle bugs that are fatal to the VM

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Date:   Tue, 29 Sep 2020 11:15:19 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Huacai Chen <chenhc@...ote.com>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        linux-mips@...r.kernel.org, Paul Mackerras <paulus@...abs.org>,
        kvm-ppc@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Subject: Re: [RFC PATCH 3/3] KVM: x86: Use KVM_BUG/KVM_BUG_ON to handle bugs
 that are fatal to the VM

On 29/09/20 05:52, Sean Christopherson wrote:
>> I think usage should be limited to dangerous cases, basically WARN_ON
>> level.  However I agree with Vitaly that KVM_GET_* should be allowed.
>
> On the topic of feedback from Vitaly, while dredging through my mailbox I
> rediscovered his suggestion of kvm->kvm_internal_bug (or maybe just
> kvm->internal_bug) instead of kvm->vm_bugged[*].

Also agrees with KVM_EXIT_INTERNAL_ERROR.

>> The other question is whether to return -EIO or KVM_EXIT_INTERNAL_ERROR.
>>  The latter is more likely to be handled already by userspace.
>
> And probably less confusing for unsuspecting users.  E.g. -EIO is most
> likely to be interpreted as "I screwed up", whereas KVM_EXIT_INTERNAL_ERROR
> will correctly be read as "KVM screwed up".

All good points, seems like you have enough review material for the
non-RFC version.

Paolo