Commit 4265df66 authored by Peng Hao's avatar Peng Hao Committed by Sean Christopherson
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KVM: x86: Keep the lock order consistent between SRCU and gpc spinlock 



Acquire SRCU before taking the gpc spinlock in wait_pending_event() so as
to be consistent with all other functions that acquire both locks.  It's
not illegal to acquire SRCU inside a spinlock, nor is there deadlock
potential, but in general it's preferable to order locks from least
restrictive to most restrictive, e.g. if wait_pending_event() needed to
sleep for whatever reason, it could do so while holding SRCU, but would
need to drop the spinlock.

Signed-off-by: default avatarPeng Hao <flyingpeng@tencent.com>
Reviewed-by: default avatarSean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/CAPm50a++Cb=QfnjMZ2EnCj-Sb9Y4UM-=uOEtHAcjnNLCAAf-dQ@mail.gmail.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent eb3992e8

arch/x86/kvm/xen.c

+2 −2
Original line number Diff line number Diff line
@@ -1165,8 +1165,8 @@ static bool wait_pending_event(struct kvm_vcpu *vcpu, int nr_ports, 
	bool ret = true;

	int idx, i;



	read_lock_irqsave(&gpc->lock, flags);

	idx = srcu_read_lock(&kvm->srcu);

	read_lock_irqsave(&gpc->lock, flags);

	if (!kvm_gpc_check(kvm, gpc, gpc->gpa, PAGE_SIZE))

		goto out_rcu;
@@ -1187,8 +1187,8 @@ static bool wait_pending_event(struct kvm_vcpu *vcpu, int nr_ports, 
	}



 out_rcu:

	srcu_read_unlock(&kvm->srcu, idx);

	read_unlock_irqrestore(&gpc->lock, flags);

	srcu_read_unlock(&kvm->srcu, idx);



	return ret;

}