KVM: PPC: Book3S HV: Speed up wakeups of CPUs on HV KVM

Currently, we wake up a CPU by sending a host IPI with
smp_send_reschedule() to thread 0 of that core, which will take all
threads out of the guest, and cause them to re-evaluate their
interrupt status on the way back in.

This adds a mechanism to differentiate real host IPIs from IPIs sent
by KVM for guest threads to poke each other, in order to target the
guest threads precisely when possible and avoid that global switch of
the core to host state.

We then use this new facility in the in-kernel XICS code.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/include/asm/kvm_book3s_asm.h

@@ -20,6 +20,11 @@
 #ifndef __ASM_KVM_BOOK3S_ASM_H__
 #define __ASM_KVM_BOOK3S_ASM_H__
 
+/* XICS ICP register offsets */
+#define XICS_XIRR		4
+#define XICS_MFRR		0xc
+#define XICS_IPI		2	/* interrupt source # for IPIs */
+
 #ifdef __ASSEMBLY__
 
 #ifdef CONFIG_KVM_BOOK3S_HANDLER
@@ -81,10 +86,11 @@ struct kvmppc_host_state {
 #ifdef CONFIG_KVM_BOOK3S_64_HV
 	u8 hwthread_req;
 	u8 hwthread_state;
-
+	u8 host_ipi;
 	struct kvm_vcpu *kvm_vcpu;
 	struct kvmppc_vcore *kvm_vcore;
 	unsigned long xics_phys;
+	u32 saved_xirr;
 	u64 dabr;
 	u64 host_mmcr[3];
 	u32 host_pmc[8];

arch/powerpc/include/asm/kvm_ppc.h

@@ -264,6 +264,21 @@ static inline void kvmppc_set_xics_phys(int cpu, unsigned long addr)
 	paca[cpu].kvm_hstate.xics_phys = addr;
 }
 
+static inline u32 kvmppc_get_xics_latch(void)
+{
+	u32 xirr = get_paca()->kvm_hstate.saved_xirr;
+
+	get_paca()->kvm_hstate.saved_xirr = 0;
+
+	return xirr;
+}
+
+static inline void kvmppc_set_host_ipi(int cpu, u8 host_ipi)
+{
+	paca[cpu].kvm_hstate.host_ipi = host_ipi;
+}
+
+extern void kvmppc_fast_vcpu_kick(struct kvm_vcpu *vcpu);
 extern void kvm_linear_init(void);
 
 #else
@@ -273,6 +288,18 @@ static inline void kvmppc_set_xics_phys(int cpu, unsigned long addr)
 static inline void kvm_linear_init(void)
 {}
 
+static inline u32 kvmppc_get_xics_latch(void)
+{
+	return 0;
+}
+
+static inline void kvmppc_set_host_ipi(int cpu, u8 host_ipi)
+{}
+
+static inline void kvmppc_fast_vcpu_kick(struct kvm_vcpu *vcpu)
+{
+	kvm_vcpu_kick(vcpu);
+}
 #endif
 
 #ifdef CONFIG_KVM_XICS
@@ -393,4 +420,6 @@ static inline ulong kvmppc_get_ea_indexed(struct kvm_vcpu *vcpu, int ra, int rb)
 	return ea;
 }
 
+extern void xics_wake_cpu(int cpu);
+
 #endif /* __POWERPC_KVM_PPC_H__ */

arch/powerpc/kernel/asm-offsets.c

@@ -574,6 +574,8 @@ int main(void)
 	HSTATE_FIELD(HSTATE_KVM_VCPU, kvm_vcpu);
 	HSTATE_FIELD(HSTATE_KVM_VCORE, kvm_vcore);
 	HSTATE_FIELD(HSTATE_XICS_PHYS, xics_phys);
+	HSTATE_FIELD(HSTATE_SAVED_XIRR, saved_xirr);
+	HSTATE_FIELD(HSTATE_HOST_IPI, host_ipi);
 	HSTATE_FIELD(HSTATE_MMCR, host_mmcr);
 	HSTATE_FIELD(HSTATE_PMC, host_pmc);
 	HSTATE_FIELD(HSTATE_PURR, host_purr);

arch/powerpc/kvm/book3s_hv.c

@@ -66,6 +66,31 @@
 static void kvmppc_end_cede(struct kvm_vcpu *vcpu);
 static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu);
 
+void kvmppc_fast_vcpu_kick(struct kvm_vcpu *vcpu)
+{
+	int me;
+	int cpu = vcpu->cpu;
+	wait_queue_head_t *wqp;
+
+	wqp = kvm_arch_vcpu_wq(vcpu);
+	if (waitqueue_active(wqp)) {
+		wake_up_interruptible(wqp);
+		++vcpu->stat.halt_wakeup;
+	}
+
+	me = get_cpu();
+
+	/* CPU points to the first thread of the core */
+	if (cpu != me && cpu >= 0 && cpu < nr_cpu_ids) {
+		int real_cpu = cpu + vcpu->arch.ptid;
+		if (paca[real_cpu].kvm_hstate.xics_phys)
+			xics_wake_cpu(real_cpu);
+		else if (cpu_online(cpu))
+			smp_send_reschedule(cpu);
+	}
+	put_cpu();
+}
+
 /*
  * We use the vcpu_load/put functions to measure stolen time.
  * Stolen time is counted as time when either the vcpu is able to
@@ -985,7 +1010,6 @@ static void kvmppc_end_cede(struct kvm_vcpu *vcpu)
 }
 
 extern int __kvmppc_vcore_entry(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu);
-extern void xics_wake_cpu(int cpu);
 
 static void kvmppc_remove_runnable(struct kvmppc_vcore *vc,
 				   struct kvm_vcpu *vcpu)

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -79,10 +79,6 @@ _GLOBAL(kvmppc_hv_entry_trampoline)
  *                                                                            *
  *****************************************************************************/
 
-#define XICS_XIRR		4
-#define XICS_QIRR		0xc
-#define XICS_IPI		2	/* interrupt source # for IPIs */
-
 /*
  * We come in here when wakened from nap mode on a secondary hw thread.
  * Relocation is off and most register values are lost.
@@ -122,7 +118,7 @@ kvm_start_guest:
 	beq	27f
 25:	ld	r5,HSTATE_XICS_PHYS(r13)
 	li	r0,0xff
-	li	r6,XICS_QIRR
+	li	r6,XICS_MFRR
 	li	r7,XICS_XIRR
 	lwzcix	r8,r5,r7		/* get and ack the interrupt */
 	sync
@@ -678,17 +674,91 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
 	cmpwi	r12,BOOK3S_INTERRUPT_SYSCALL
 	beq	hcall_try_real_mode
 
-	/* Check for mediated interrupts (could be done earlier really ...) */
+	/* Only handle external interrupts here on arch 206 and later */
 BEGIN_FTR_SECTION
-	cmpwi	r12,BOOK3S_INTERRUPT_EXTERNAL
-	bne+	1f
-	andi.	r0,r11,MSR_EE
-	beq	1f
-	mfspr	r5,SPRN_LPCR
-	andi.	r0,r5,LPCR_MER
+	b	ext_interrupt_to_host
+END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
+
+	/* External interrupt ? */
+	cmpwi	r12, BOOK3S_INTERRUPT_EXTERNAL
+	bne+	ext_interrupt_to_host
+
+	/* External interrupt, first check for host_ipi. If this is
+	 * set, we know the host wants us out so let's do it now
+	 */
+	lbz	r0, HSTATE_HOST_IPI(r13)
+	cmpwi	r0, 0
+	bne	ext_interrupt_to_host
+
+	/* Now read the interrupt from the ICP */
+	ld	r5, HSTATE_XICS_PHYS(r13)
+	li	r7, XICS_XIRR
+	cmpdi	r5, 0
+	beq-	ext_interrupt_to_host
+	lwzcix	r3, r5, r7
+	rlwinm.	r0, r3, 0, 0xffffff
+	sync
+	bne	1f
+
+	/* 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
-1:
-END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
+	b	ext_interrupt_to_host /* shouldn't happen ?? */
+
+1:	/* 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
+	 * interrupts directly to the guest
+	 */
+	cmpwi	r0, XICS_IPI
+	bne	ext_stash_for_host
+
+	/* It's an IPI, clear the MFRR and EOI it */
+	li	r0, 0xff
+	li	r6, XICS_MFRR
+	stbcix	r0, r5, r6		/* clear the IPI */
+	stwcix	r3, r5, r7		/* EOI it */
+	sync
+
+	/* We need to re-check host IPI now in case it got set in the
+	 * meantime. If it's clear, we bounce the interrupt to the
+	 * guest
+	 */
+	lbz	r0, HSTATE_HOST_IPI(r13)
+	cmpwi	r0, 0
+	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
+
+	/* 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
+	b	fast_guest_return
+
+	/* We raced with the host, we need to resend that IPI, bummer */
+1:	li	r0, IPI_PRIORITY
+	stbcix	r0, r5, r6		/* set the IPI */
+	sync
+	b	ext_interrupt_to_host
+
+ext_stash_for_host:
+	/* It's not an IPI and it's for the host, stash it in the PACA
+	 * before exit, it will be picked up by the host ICP driver
+	 */
+	stw	r3, HSTATE_SAVED_XIRR(r13)
+ext_interrupt_to_host:
 
 guest_exit_cont:		/* r9 = vcpu, r12 = trap, r13 = paca */
 	/* Save DEC */
@@ -831,7 +901,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201)
 	beq	44f
 	ld	r8,HSTATE_XICS_PHYS(r6)	/* get thread's XICS reg addr */
 	li	r0,IPI_PRIORITY
-	li	r7,XICS_QIRR
+	li	r7,XICS_MFRR
 	stbcix	r0,r7,r8		/* trigger the IPI */
 44:	srdi.	r3,r3,1
 	addi	r6,r6,PACA_SIZE
@@ -1630,7 +1700,7 @@ secondary_nap:
 	beq	37f
 	sync
 	li	r0, 0xff
-	li	r6, XICS_QIRR
+	li	r6, XICS_MFRR
 	stbcix	r0, r5, r6		/* clear the IPI */
 	stwcix	r3, r5, r7		/* EOI it */
 37:	sync

arch/powerpc/kvm/book3s_xics.c

@@ -227,7 +227,7 @@ static inline bool icp_try_update(struct kvmppc_icp *icp,
 		kvmppc_book3s_queue_irqprio(icp->vcpu,
 					    BOOK3S_INTERRUPT_EXTERNAL_LEVEL);
 		if (!change_self)
-			kvm_vcpu_kick(icp->vcpu);
+			kvmppc_fast_vcpu_kick(icp->vcpu);
 	}
  bail:
 	return success;

arch/powerpc/sysdev/xics/icp-native.c

@@ -51,6 +51,12 @@ static struct icp_ipl __iomem *icp_native_regs[NR_CPUS];
 static inline unsigned int icp_native_get_xirr(void)
 {
 	int cpu = smp_processor_id();
+	unsigned int xirr;
+
+	/* Handled an interrupt latched by KVM */
+	xirr = kvmppc_get_xics_latch();
+	if (xirr)
+		return xirr;
 
 	return in_be32(&icp_native_regs[cpu]->xirr.word);
 }
@@ -138,6 +144,7 @@ static unsigned int icp_native_get_irq(void)
 
 static void icp_native_cause_ipi(int cpu, unsigned long data)
 {
+	kvmppc_set_host_ipi(cpu, 1);
 	icp_native_set_qirr(cpu, IPI_PRIORITY);
 }
 
@@ -151,6 +158,7 @@ static irqreturn_t icp_native_ipi_action(int irq, void *dev_id)
 {
 	int cpu = smp_processor_id();
 
+	kvmppc_set_host_ipi(cpu, 0);
 	icp_native_set_qirr(cpu, 0xff);
 
 	return smp_ipi_demux();