powerpc/kvm/book3s_hv: Use threads_per_subcore in KVM

To support split core on POWER8 we need to modify various parts of the
KVM code to use threads_per_subcore instead of threads_per_core. On
systems that do not support split core threads_per_subcore ==
threads_per_core and these changes are a nop.

We use threads_per_subcore as the value reported by KVM_CAP_PPC_SMT.
This communicates to userspace that guests can only be created with
a value of threads_per_core that is less than or equal to the current
threads_per_subcore. This ensures that guests can only be created with a
thread configuration that we are able to run given the current split
core mode.

Although threads_per_subcore can change during the life of the system,
the commit that enables that will ensure that threads_per_subcore does
not change during the life of a KVM VM.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Acked-by: Alexander Graf <agraf@suse.de>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 16 insertions, 10 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index d7b74f888ad8..5e86f28c9d2f 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1266,7 +1266,7 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
         int core;
         struct kvmppc_vcore *vcore;
 
-        core = id / threads_per_core;
+        core = id / threads_per_subcore;
         if (core >= KVM_MAX_VCORES)
                 goto out;
 
@@ -1305,7 +1305,7 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
                         init_waitqueue_head(&vcore->wq);
                         vcore->preempt_tb = TB_NIL;
                         vcore->lpcr = kvm->arch.lpcr;
-                        vcore->first_vcpuid = core * threads_per_core;
+                        vcore->first_vcpuid = core * threads_per_subcore;
                         vcore->kvm = kvm;
                 }
                 kvm->arch.vcores[core] = vcore;
@@ -1495,16 +1495,19 @@ static void kvmppc_wait_for_nap(struct kvmppc_vcore *vc)
 static int on_primary_thread(void)
 {
         int cpu = smp_processor_id();
-        int thr = cpu_thread_in_core(cpu);
+        int thr;
 
-        if (thr)
+        /* Are we on a primary subcore? */
+        if (cpu_thread_in_subcore(cpu))
                 return 0;
-        while (++thr < threads_per_core)
+
+        thr = 0;
+        while (++thr < threads_per_subcore)
                 if (cpu_online(cpu + thr))
                         return 0;
 
         /* Grab all hw threads so they can't go into the kernel */
-        for (thr = 1; thr < threads_per_core; ++thr) {
+        for (thr = 1; thr < threads_per_subcore; ++thr) {
                 if (kvmppc_grab_hwthread(cpu + thr)) {
                         /* Couldn't grab one; let the others go */
                         do {
@@ -1563,15 +1566,18 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc)
         }
 
         /*
-         * Make sure we are running on thread 0, and that
-         * secondary threads are offline.
+         * Make sure we are running on primary threads, and that secondary
+         * threads are offline.  Also check if the number of threads in this
+         * guest are greater than the current system threads per guest.
          */
-        if (threads_per_core > 1 && !on_primary_thread()) {
+        if ((threads_per_core > 1) &&
+            ((vc->num_threads > threads_per_subcore) || !on_primary_thread())) {
                 list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
                         vcpu->arch.ret = -EBUSY;
                 goto out;
         }
 
+
         vc->pcpu = smp_processor_id();
         list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list) {
                 kvmppc_start_thread(vcpu);
@@ -1599,7 +1605,7 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc)
         /* wait for secondary threads to finish writing their state to memory */
         if (vc->nap_count < vc->n_woken)
                 kvmppc_wait_for_nap(vc);
-        for (i = 0; i < threads_per_core; ++i)
+        for (i = 0; i < threads_per_subcore; ++i)
                 kvmppc_release_hwthread(vc->pcpu + i);
         /* prevent other vcpu threads from doing kvmppc_start_thread() now */
         vc->vcore_state = VCORE_EXITING;