KVM: PPC: Book3S HV: Improve real-mode handling of external interrupts

This streamlines our handling of external interrupts that come in
while we're in the guest.  First, when waking up a hardware thread
that was napping, we split off the "napping due to H_CEDE" case
earlier, and use the code that handles an external interrupt (0x500)
in the guest to handle that too.  Secondly, the code that handles
those external interrupts now checks if any other thread is exiting
to the host before bouncing an external interrupt to the guest, and
also checks that there is actually an external interrupt pending for
the guest before setting the LPCR MER bit (mediated external request).

This also makes sure that we clear the "ceded" flag when we handle a
wakeup from cede in real mode, and fixes a potential infinite loop
in kvmppc_run_vcpu() which can occur if we ever end up with the ceded
flag set but MSR[EE] off.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/include/asm/reg.h

@@ -290,6 +290,7 @@
 #define     LPCR_PECE1	0x00002000	/* decrementer can cause exit */
 #define     LPCR_PECE2	0x00001000	/* machine check etc can cause exit */
 #define   LPCR_MER	0x00000800	/* Mediated External Exception */
+#define   LPCR_MER_SH	11
 #define   LPCR_LPES    0x0000000c
 #define   LPCR_LPES0   0x00000008      /* LPAR Env selector 0 */
 #define   LPCR_LPES1   0x00000004      /* LPAR Env selector 1 */

arch/powerpc/kvm/book3s_hv.c

@@ -1384,9 +1384,12 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 			break;
 		vc->runner = vcpu;
 		n_ceded = 0;
-		list_for_each_entry(v, &vc->runnable_threads, arch.run_list)
+		list_for_each_entry(v, &vc->runnable_threads, arch.run_list) {
 			if (!v->arch.pending_exceptions)
 				n_ceded += v->arch.ceded;
+			else
+				v->arch.ceded = 0;
+		}
 		if (n_ceded == vc->n_runnable)
 			kvmppc_vcore_blocked(vc);
 		else

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -97,50 +97,51 @@ kvm_start_guest:
 	li	r0,1
 	stb	r0,PACA_NAPSTATELOST(r13)
 
-	/* get vcpu pointer, NULL if we have no vcpu to run */
-	ld	r4,HSTATE_KVM_VCPU(r13)
-	cmpdi	cr1,r4,0
+	/* were we napping due to cede? */
+	lbz	r0,HSTATE_NAPPING(r13)
+	cmpwi	r0,0
+	bne	kvm_end_cede
+
+	/*
+	 * We weren't napping due to cede, so this must be a secondary
+	 * thread being woken up to run a guest, or being woken up due
+	 * to a stray IPI.  (Or due to some machine check or hypervisor
+	 * maintenance interrupt while the core is in KVM.)
+	 */
 
 	/* Check the wake reason in SRR1 to see why we got here */
 	mfspr	r3,SPRN_SRR1
 	rlwinm	r3,r3,44-31,0x7		/* extract wake reason field */
 	cmpwi	r3,4			/* was it an external interrupt? */
-	bne	27f
-
-	/*
-	 * External interrupt - for now assume it is an IPI, since we
-	 * should never get any other interrupts sent to offline threads.
-	 * Only do this for secondary threads.
-	 */
-	beq	cr1,25f
-	lwz	r3,VCPU_PTID(r4)
-	cmpwi	r3,0
-	beq	27f
-25:	ld	r5,HSTATE_XICS_PHYS(r13)
-	li	r0,0xff
-	li	r6,XICS_MFRR
-	li	r7,XICS_XIRR
+	bne	27f			/* if not */
+	ld	r5,HSTATE_XICS_PHYS(r13)
+	li	r7,XICS_XIRR		/* if it was an external interrupt, */
 	lwzcix	r8,r5,r7		/* get and ack the interrupt */
 	sync
 	clrldi.	r9,r8,40		/* get interrupt source ID. */
-	beq	27f			/* none there? */
-	cmpwi	r9,XICS_IPI
-	bne	26f
+	beq	28f			/* none there? */
+	cmpwi	r9,XICS_IPI		/* was it an IPI? */
+	bne	29f
+	li	r0,0xff
+	li	r6,XICS_MFRR
 	stbcix	r0,r5,r6		/* clear IPI */
-26:	stwcix	r8,r5,r7		/* EOI the interrupt */
+	stwcix	r8,r5,r7		/* EOI the interrupt */
+	sync				/* order loading of vcpu after that */
 
-27:	/* XXX should handle hypervisor maintenance interrupts etc. here */
-
-	/* reload vcpu pointer after clearing the IPI */
+	/* get vcpu pointer, NULL if we have no vcpu to run */
 	ld	r4,HSTATE_KVM_VCPU(r13)
 	cmpdi	r4,0
 	/* if we have no vcpu to run, go back to sleep */
 	beq	kvm_no_guest
+	b	kvmppc_hv_entry
 
-	/* were we napping due to cede? */
-	lbz	r0,HSTATE_NAPPING(r13)
-	cmpwi	r0,0
-	bne	kvm_end_cede
+27:	/* XXX should handle hypervisor maintenance interrupts etc. here */
+	b	kvm_no_guest
+28:	/* SRR1 said external but ICP said nope?? */
+	b	kvm_no_guest
+29:	/* External non-IPI interrupt to offline secondary thread? help?? */
+	stw	r8,HSTATE_SAVED_XIRR(r13)
+	b	kvm_no_guest
 
 .global kvmppc_hv_entry
 kvmppc_hv_entry:
@@ -483,20 +484,20 @@ toc_tlbie_lock:
 	mtctr	r6
 	mtxer	r7
 
+	ld	r10, VCPU_PC(r4)
+	ld	r11, VCPU_MSR(r4)
 kvmppc_cede_reentry:		/* r4 = vcpu, r13 = paca */
 	ld	r6, VCPU_SRR0(r4)
 	ld	r7, VCPU_SRR1(r4)
-	ld	r10, VCPU_PC(r4)
-	ld	r11, VCPU_MSR(r4)	/* r11 = vcpu->arch.msr & ~MSR_HV */
 
+	/* r11 = vcpu->arch.msr & ~MSR_HV */
 	rldicl	r11, r11, 63 - MSR_HV_LG, 1
 	rotldi	r11, r11, 1 + MSR_HV_LG
 	ori	r11, r11, MSR_ME
 
 	/* Check if we can deliver an external or decrementer interrupt now */
 	ld	r0,VCPU_PENDING_EXC(r4)
-	li	r8,(1 << BOOK3S_IRQPRIO_EXTERNAL)
-	oris	r8,r8,(1 << BOOK3S_IRQPRIO_EXTERNAL_LEVEL)@h
+	lis	r8,(1 << BOOK3S_IRQPRIO_EXTERNAL_LEVEL)@h
 	and	r0,r0,r8
 	cmpdi	cr1,r0,0
 	andi.	r0,r11,MSR_EE
@@ -524,10 +525,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
 	/* Move SRR0 and SRR1 into the respective regs */
 5:	mtspr	SPRN_SRR0, r6
 	mtspr	SPRN_SRR1, r7
-	li	r0,0
-	stb	r0,VCPU_CEDED(r4)	/* cancel cede */
 
 fast_guest_return:
+	li	r0,0
+	stb	r0,VCPU_CEDED(r4)	/* cancel cede */
 	mtspr	SPRN_HSRR0,r10
 	mtspr	SPRN_HSRR1,r11
 
@@ -686,6 +687,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
 	/* External interrupt, first check for host_ipi. If this is
 	 * set, we know the host wants us out so let's do it now
 	 */
+do_ext_interrupt:
 	lbz	r0, HSTATE_HOST_IPI(r13)
 	cmpwi	r0, 0
 	bne	ext_interrupt_to_host
@@ -698,19 +700,9 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
 	lwzcix	r3, r5, r7
 	rlwinm.	r0, r3, 0, 0xffffff
 	sync
-	bne	1f
+	beq	3f		/* if nothing pending in the ICP */
 
-	/* Nothing pending in the ICP, check for mediated interrupts
-	 * and bounce it to the guest
-	 */
-	andi.	r0, r11, MSR_EE
-	beq	ext_interrupt_to_host /* shouldn't happen ?? */
-	mfspr	r5, SPRN_LPCR
-	andi.	r0, r5, LPCR_MER
-	bne	bounce_ext_interrupt
-	b	ext_interrupt_to_host /* shouldn't happen ?? */
-
-1:	/* We found something in the ICP...
+	/* We found something in the ICP...
 	 *
 	 * If it's not an IPI, stash it in the PACA and return to
 	 * the host, we don't (yet) handle directing real external
@@ -735,16 +727,33 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
 	bne-	1f
 
 	/* Allright, looks like an IPI for the guest, we need to set MER */
-	mfspr	r8,SPRN_LPCR
-	ori	r8,r8,LPCR_MER
-	mtspr	SPRN_LPCR,r8
+3:
+	/* Check if any CPU is heading out to the host, if so head out too */
+	ld	r5, HSTATE_KVM_VCORE(r13)
+	lwz	r0, VCORE_ENTRY_EXIT(r5)
+	cmpwi	r0, 0x100
+	bge	ext_interrupt_to_host
+
+	/* See if there is a pending interrupt for the guest */
+	mfspr	r8, SPRN_LPCR
+	ld	r0, VCPU_PENDING_EXC(r9)
+	/* Insert EXTERNAL_LEVEL bit into LPCR at the MER bit position */
+	rldicl.	r0, r0, 64 - BOOK3S_IRQPRIO_EXTERNAL_LEVEL, 63
+	rldimi	r8, r0, LPCR_MER_SH, 63 - LPCR_MER_SH
+	beq	2f
 
 	/* And if the guest EE is set, we can deliver immediately, else
 	 * we return to the guest with MER set
 	 */
 	andi.	r0, r11, MSR_EE
-	bne	bounce_ext_interrupt
-	mr	r4, r9
+	beq	2f
+	mtspr	SPRN_SRR0, r10
+	mtspr	SPRN_SRR1, r11
+	li	r10, BOOK3S_INTERRUPT_EXTERNAL
+	li	r11, (MSR_ME << 1) | 1	/* synthesize MSR_SF | MSR_ME */
+	rotldi	r11, r11, 63
+2:	mr	r4, r9
+	mtspr	SPRN_LPCR, r8
 	b	fast_guest_return
 
 	/* We raced with the host, we need to resend that IPI, bummer */
@@ -1487,15 +1496,6 @@ ignore_hdec:
 	mr	r4,r9
 	b	fast_guest_return
 
-bounce_ext_interrupt:
-	mr	r4,r9
-	mtspr	SPRN_SRR0,r10
-	mtspr	SPRN_SRR1,r11
-	li	r10,BOOK3S_INTERRUPT_EXTERNAL
-	li	r11,(MSR_ME << 1) | 1	/* synthesize MSR_SF | MSR_ME */
-	rotldi	r11,r11,63
-	b	fast_guest_return
-
 _GLOBAL(kvmppc_h_set_dabr)
 	std	r4,VCPU_DABR(r3)
 	/* Work around P7 bug where DABR can get corrupted on mtspr */
@@ -1601,6 +1601,9 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
 	b	.
 
 kvm_end_cede:
+	/* get vcpu pointer */
+	ld	r4, HSTATE_KVM_VCPU(r13)
+
 	/* Woken by external or decrementer interrupt */
 	ld	r1, HSTATE_HOST_R1(r13)
 
@@ -1640,6 +1643,16 @@ kvm_end_cede:
 	li	r0,0
 	stb	r0,HSTATE_NAPPING(r13)
 
+	/* Check the wake reason in SRR1 to see why we got here */
+	mfspr	r3, SPRN_SRR1
+	rlwinm	r3, r3, 44-31, 0x7	/* extract wake reason field */
+	cmpwi	r3, 4			/* was it an external interrupt? */
+	li	r12, BOOK3S_INTERRUPT_EXTERNAL
+	mr	r9, r4
+	ld	r10, VCPU_PC(r9)
+	ld	r11, VCPU_MSR(r9)
+	beq	do_ext_interrupt	/* if so */
+
 	/* see if any other thread is already exiting */
 	lwz	r0,VCORE_ENTRY_EXIT(r5)
 	cmpwi	r0,0x100
@@ -1659,8 +1672,7 @@ kvm_cede_prodded:
 
 	/* we've ceded but we want to give control to the host */
 kvm_cede_exit:
-	li	r3,H_TOO_HARD
-	blr
+	b	hcall_real_fallback
 
 	/* Try to handle a machine check in real mode */
 machine_check_realmode: