KVM: PPC: Book3S: PR: Rework irq disabling

Today, we disable preemption while inside guest context, because we need
to expose to the world that we are not in a preemptible context. However,
during that time we already have interrupts disabled, which would indicate
that we are in a non-preemptible context.

The reason the checks for irqs_disabled() fail for us though is that we
manually control hard IRQs and ignore all the lazy EE framework. Let's
stop doing that. Instead, let's always use lazy EE to indicate when we
want to disable IRQs, but do a special final switch that gets us into
EE disabled, but soft enabled state. That way when we get back out of
guest state, we are immediately ready to process interrupts.

This simplifies the code drastically and reduces the time that we appear
as preempt disabled.

Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 8 insertions, 7 deletions

diff --git a/arch/powerpc/kvm/book3s_rmhandlers.S b/arch/powerpc/kvm/book3s_rmhandlers.S
index 9ecf6e35cd8..b2f8258b545 100644
--- a/arch/powerpc/kvm/book3s_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_rmhandlers.S
@@ -170,20 +170,21 @@ kvmppc_handler_skip_ins:
  * Call kvmppc_handler_trampoline_enter in real mode
  *
  * On entry, r4 contains the guest shadow MSR
+ * MSR.EE has to be 0 when calling this function
  */
 _GLOBAL(kvmppc_entry_trampoline)
 	mfmsr	r5
 	LOAD_REG_ADDR(r7, kvmppc_handler_trampoline_enter)
 	toreal(r7)
 
-	li	r9, MSR_RI
-	ori	r9, r9, MSR_EE
-	andc	r9, r5, r9	/* Clear EE and RI in MSR value */
 	li	r6, MSR_IR | MSR_DR
-	ori	r6, r6, MSR_EE
-	andc	r6, r5, r6	/* Clear EE, DR and IR in MSR value */
-	MTMSR_EERI(r9)		/* Clear EE and RI in MSR */
-	mtsrr0	r7		/* before we set srr0/1 */
+	andc	r6, r5, r6	/* Clear DR and IR in MSR value */
+	/*
+	 * Set EE in HOST_MSR so that it's enabled when we get into our
+	 * C exit handler function
+	 */
+	ori	r5, r5, MSR_EE
+	mtsrr0	r7
 	mtsrr1	r6
 	RFI