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[PATCH v2 2/2] KVM: async_pf: rcu irq exit if not triggered from idle task

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From: Wanpeng Li <wanpeng.li@hotmail.com>

Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault) 
adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs 
when needed, to protect the code that needs use rcu. There is no need to call 
this pairs if async page fault is not triggered from idle task.

This patch invokes rcu irq exit if it is not triggered from idle task.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v1 -> v2:
 * update patch description

 arch/x86/kernel/kvm.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 43e10d6..e70ed72 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -141,6 +141,8 @@ void kvm_async_pf_task_wait(u32 token)
 	n.token = token;
 	n.cpu = smp_processor_id();
 	n.halted = is_idle_task(current) || preempt_count() > 1;
+	if (!n.halted)
+		rcu_irq_exit();
 	init_swait_queue_head(&n.wq);
 	hlist_add_head(&n.link, &b->list);
 	raw_spin_unlock(&b->lock);
@@ -167,8 +169,9 @@ void kvm_async_pf_task_wait(u32 token)
 	}
 	if (!n.halted)
 		finish_swait(&n.wq, &wait);
+	else
+		rcu_irq_exit();
 
-	rcu_irq_exit();
 	return;
 }
 EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
-- 
2.7.4

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[PATCH v2 1/2] KVM: cpuid: Fix read/write out-of-bounds vulnerability in cpuid emulation Wanpeng Li <kernellwp@gmail.com> - 2017-06-08 10:30 +0200
  [PATCH v2 2/2] KVM: async_pf: rcu irq exit if not triggered from idle task Wanpeng Li <kernellwp@gmail.com> - 2017-06-08 10:30 +0200
  Re: [PATCH v2 1/2] KVM: cpuid: Fix read/write out-of-bounds  vulnerability in cpuid emulation Paolo Bonzini <pbonzini@redhat.com> - 2017-06-08 15:40 +0200

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