linux-kernel - Re: [PATCH v3] KVM: SEV: Mark nested locking of vcpu->lock

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Message-ID: <62e9ece1-5d71-f803-3f65-2755160cf1d1@redhat.com>
Date:   Thu, 21 Apr 2022 17:56:52 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Gonda <pgonda@...gle.com>,
        John Sperbeck <jsperbeck@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] KVM: SEV: Mark nested locking of vcpu->lock

On 4/20/22 22:14, Peter Gonda wrote:
>>>> svm_vm_migrate_from() uses sev_lock_vcpus_for_migration() to lock all
>>>> source and target vcpu->locks. Mark the nested subclasses to avoid false
>>>> positives from lockdep.
>> Nope. Good catch, I didn't realize there was a limit 8 subclasses:
> Does anyone have thoughts on how we can resolve this vCPU locking with
> the 8 subclass max?

The documentation does not have anything.  Maybe you can call 
mutex_release manually (and mutex_acquire before unlocking).

Paolo