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Commit 5d5b99cd authored by Paul Mackerras's avatar Paul Mackerras Committed by Alexander Graf
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KVM: PPC: Book3S HV: Get rid of vcore nap_count and n_woken 



We can tell when a secondary thread has finished running a guest by
the fact that it clears its kvm_hstate.kvm_vcpu pointer, so there
is no real need for the nap_count field in the kvmppc_vcore struct.
This changes kvmppc_wait_for_nap to poll the kvm_hstate.kvm_vcpu
pointers of the secondary threads rather than polling vc->nap_count.
Besides reducing the size of the kvmppc_vcore struct by 8 bytes,
this also means that we can tell which secondary threads have got
stuck and thus print a more informative error message.

Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
parent 25fedfca

arch/powerpc/include/asm/kvm_host.h

+0 −2
Original line number Diff line number Diff line
@@ -272,8 +272,6 @@ struct kvmppc_vcore { 
	int n_runnable;

	int num_threads;

	int entry_exit_count;

	int n_woken;

	int nap_count;

	int napping_threads;

	int first_vcpuid;

	u16 pcpu;

arch/powerpc/kernel/asm-offsets.c

+0 −1
Original line number Diff line number Diff line
@@ -563,7 +563,6 @@ int main(void) 
	DEFINE(VCPU_WORT, offsetof(struct kvm_vcpu, arch.wort));

	DEFINE(VCPU_SHADOW_SRR1, offsetof(struct kvm_vcpu, arch.shadow_srr1));

	DEFINE(VCORE_ENTRY_EXIT, offsetof(struct kvmppc_vcore, entry_exit_count));

	DEFINE(VCORE_NAP_COUNT, offsetof(struct kvmppc_vcore, nap_count));

	DEFINE(VCORE_IN_GUEST, offsetof(struct kvmppc_vcore, in_guest));

	DEFINE(VCORE_NAPPING_THREADS, offsetof(struct kvmppc_vcore, napping_threads));

	DEFINE(VCORE_KVM, offsetof(struct kvmppc_vcore, kvm));

arch/powerpc/kvm/book3s_hv.c

+27 −20
Original line number Diff line number Diff line
@@ -1729,8 +1729,10 @@ static int kvmppc_grab_hwthread(int cpu) 
	tpaca = &paca[cpu];



	/* Ensure the thread won't go into the kernel if it wakes */

	tpaca->kvm_hstate.hwthread_req = 1;

	tpaca->kvm_hstate.kvm_vcpu = NULL;

	tpaca->kvm_hstate.napping = 0;

	smp_wmb();

	tpaca->kvm_hstate.hwthread_req = 1;



	/*

	 * If the thread is already executing in the kernel (e.g. handling
@@ -1773,35 +1775,43 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu) 
	}

	cpu = vc->pcpu + vcpu->arch.ptid;

	tpaca = &paca[cpu];

	tpaca->kvm_hstate.kvm_vcpu = vcpu;

	tpaca->kvm_hstate.kvm_vcore = vc;

	tpaca->kvm_hstate.ptid = vcpu->arch.ptid;

	vcpu->cpu = vc->pcpu;

	/* Order stores to hstate.kvm_vcore etc. before store to kvm_vcpu */

	smp_wmb();

	tpaca->kvm_hstate.kvm_vcpu = vcpu;

#if defined(CONFIG_PPC_ICP_NATIVE) && defined(CONFIG_SMP)

	if (cpu != smp_processor_id()) {

	if (cpu != smp_processor_id())

		xics_wake_cpu(cpu);

		if (vcpu->arch.ptid)

			++vc->n_woken;

	}

#endif

}



static void kvmppc_wait_for_nap(struct kvmppc_vcore *vc)

static void kvmppc_wait_for_nap(void)

{

	int i;

	int cpu = smp_processor_id();

	int i, loops;



	HMT_low();

	i = 0;

	while (vc->nap_count < vc->n_woken) {

		if (++i >= 1000000) {

			pr_err("kvmppc_wait_for_nap timeout %d %d\n",

			       vc->nap_count, vc->n_woken);

	for (loops = 0; loops < 1000000; ++loops) {

		/*

		 * Check if all threads are finished.

		 * We set the vcpu pointer when starting a thread

		 * and the thread clears it when finished, so we look

		 * for any threads that still have a non-NULL vcpu ptr.

		 */

		for (i = 1; i < threads_per_subcore; ++i)

			if (paca[cpu + i].kvm_hstate.kvm_vcpu)

				break;

		if (i == threads_per_subcore) {

			HMT_medium();

			return;

		}

		cpu_relax();

		HMT_low();

	}

	HMT_medium();

	for (i = 1; i < threads_per_subcore; ++i)

		if (paca[cpu + i].kvm_hstate.kvm_vcpu)

			pr_err("KVM: CPU %d seems to be stuck\n", cpu + i);

}



/*
@@ -1942,8 +1952,6 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc) 
	/*

	 * Initialize *vc.

	 */

	vc->n_woken = 0;

	vc->nap_count = 0;

	vc->entry_exit_count = 0;

	vc->preempt_tb = TB_NIL;

	vc->in_guest = 0;
@@ -2002,8 +2010,7 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc) 
	list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)

		vcpu->cpu = -1;

	/* wait for secondary threads to finish writing their state to memory */

	if (vc->nap_count < vc->n_woken)

		kvmppc_wait_for_nap(vc);

	kvmppc_wait_for_nap();

	for (i = 0; i < threads_per_subcore; ++i)

		kvmppc_release_hwthread(vc->pcpu + i);

	/* prevent other vcpu threads from doing kvmppc_start_thread() now */

arch/powerpc/kvm/book3s_hv_rmhandlers.S

+7 −12
Original line number Diff line number Diff line
@@ -292,26 +292,21 @@ kvm_secondary_got_guest: 
	ld	r6, PACA_DSCR(r13)

	std	r6, HSTATE_DSCR(r13)



	/* Order load of vcore, ptid etc. after load of vcpu */

	lwsync

	bl	kvmppc_hv_entry



	/* Back from the guest, go back to nap */

	/* Clear our vcpu pointer so we don't come back in early */

	li	r0, 0

	std	r0, HSTATE_KVM_VCPU(r13)

	/*

	 * Make sure we clear HSTATE_KVM_VCPU(r13) before incrementing

	 * the nap_count, because once the increment to nap_count is

	 * visible we could be given another vcpu.

	 * Once we clear HSTATE_KVM_VCPU(r13), the code in

	 * kvmppc_run_core() is going to assume that all our vcpu

	 * state is visible in memory.  This lwsync makes sure

	 * that that is true.

	 */

	lwsync



	/* increment the nap count and then go to nap mode */

	ld	r4, HSTATE_KVM_VCORE(r13)

	addi	r4, r4, VCORE_NAP_COUNT

51:	lwarx	r3, 0, r4

	addi	r3, r3, 1

	stwcx.	r3, 0, r4

	bne	51b

	std	r0, HSTATE_KVM_VCPU(r13)



/*

 * At this point we have finished executing in the guest.