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Commit 3102f784 authored by Michael Ellerman's avatar Michael Ellerman Committed by Benjamin Herrenschmidt
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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: default avatarMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
Acked-by: default avatarAlexander Graf <agraf@suse.de>
Acked-by: default avatarPaul Mackerras <paulus@samba.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 6f5e40a3

arch/powerpc/kvm/book3s_hv.c

+16 −10
Original line number Diff line number Diff line
@@ -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;

arch/powerpc/kvm/powerpc.c

+1 −1
Original line number Diff line number Diff line
@@ -384,7 +384,7 @@ int kvm_dev_ioctl_check_extension(long ext) 
#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE

	case KVM_CAP_PPC_SMT:

		if (hv_enabled)

			r = threads_per_core;

			r = threads_per_subcore;

		else

			r = 0;

		break;