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>

3 files changed, 112 insertions, 18 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 82ba00f68b07..16191915e8d0 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/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)
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 0f23bb851711..56f8927b0ddf 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/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
diff --git a/arch/powerpc/kvm/book3s_xics.c b/arch/powerpc/kvm/book3s_xics.c
index 53af848116f2..1417e65b6bbd 100644
--- a/arch/powerpc/kvm/book3s_xics.c
+++ b/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;