tree 9624c611a13ad720ec5593df5cccf04afef21bc1
parent 0d4ee88d92884c661fcafd5576da243aa943dc24
author Paul Mackerras <paulus@ozlabs.org> 1559094840 +1000
committer Paul Mackerras <paulus@ozlabs.org> 1559101476 +1000

KVM: PPC: Book3S: Use new mutex to synchronize access to rtas token list

Currently the Book 3S KVM code uses kvm->lock to synchronize access
to the kvm->arch.rtas_tokens list.  Because this list is scanned
inside kvmppc_rtas_hcall(), which is called with the vcpu mutex held,
taking kvm->lock cause a lock inversion problem, which could lead to
a deadlock.

To fix this, we add a new mutex, kvm->arch.rtas_token_lock, which nests
inside the vcpu mutexes, and use that instead of kvm->lock when
accessing the rtas token list.

This removes the lockdep_assert_held() in kvmppc_rtas_tokens_free().
At this point we don't hold the new mutex, but that is OK because
kvmppc_rtas_tokens_free() is only called when the whole VM is being
destroyed, and at that point nothing can be looking up a token in
the list.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>