KVM: PPC: Book3S HV: Take the SRCU read lock before looking up memslots

The generic KVM code uses SRCU (sleeping RCU) to protect accesses
to the memslots data structures against updates due to userspace
adding, modifying or removing memory slots.  We need to do that too,
both to avoid accessing stale copies of the memslots and to avoid
lockdep warnings.  This therefore adds srcu_read_lock/unlock pairs
around code that accesses and uses memslots.

Since the real-mode handlers for H_ENTER, H_REMOVE and H_BULK_REMOVE
need to access the memslots, and we don't want to call the SRCU code
in real mode (since we have no assurance that it would only access
the linear mapping), we hold the SRCU read lock for the VM while
in the guest.  This does mean that adding or removing memory slots
while some vcpus are executing in the guest will block for up to
two jiffies.  This tradeoff is acceptable since adding/removing
memory slots only happens rarely, while H_ENTER/H_REMOVE/H_BULK_REMOVE
are performance-critical hot paths.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -24,6 +24,7 @@
 #include <linux/slab.h>
 #include <linux/hugetlb.h>
 #include <linux/vmalloc.h>
+#include <linux/srcu.h>
 
 #include <asm/tlbflush.h>
 #include <asm/kvm_ppc.h>
@@ -1057,20 +1058,22 @@ void *kvmppc_pin_guest_page(struct kvm *kvm, unsigned long gpa,
 	unsigned long hva, psize, offset;
 	unsigned long pa;
 	unsigned long *physp;
+	int srcu_idx;
 
+	srcu_idx = srcu_read_lock(&kvm->srcu);
 	memslot = gfn_to_memslot(kvm, gfn);
 	if (!memslot || (memslot->flags & KVM_MEMSLOT_INVALID))
-		return NULL;
+		goto err;
 	if (!kvm->arch.using_mmu_notifiers) {
 		physp = kvm->arch.slot_phys[memslot->id];
 		if (!physp)
-			return NULL;
+			goto err;
 		physp += gfn - memslot->base_gfn;
 		pa = *physp;
 		if (!pa) {
 			if (kvmppc_get_guest_page(kvm, gfn, memslot,
 						  PAGE_SIZE) < 0)
-				return NULL;
+				goto err;
 			pa = *physp;
 		}
 		page = pfn_to_page(pa >> PAGE_SHIFT);
@@ -1079,9 +1082,11 @@ void *kvmppc_pin_guest_page(struct kvm *kvm, unsigned long gpa,
 		hva = gfn_to_hva_memslot(memslot, gfn);
 		npages = get_user_pages_fast(hva, 1, 1, pages);
 		if (npages < 1)
-			return NULL;
+			goto err;
 		page = pages[0];
 	}
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+
 	psize = PAGE_SIZE;
 	if (PageHuge(page)) {
 		page = compound_head(page);
@@ -1091,6 +1096,10 @@ void *kvmppc_pin_guest_page(struct kvm *kvm, unsigned long gpa,
 	if (nb_ret)
 		*nb_ret = psize - offset;
 	return page_address(page) + offset;
+
+ err:
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+	return NULL;
 }
 
 void kvmppc_unpin_guest_page(struct kvm *kvm, void *va)

arch/powerpc/kvm/book3s_hv.c

@@ -30,6 +30,7 @@
 #include <linux/cpumask.h>
 #include <linux/spinlock.h>
 #include <linux/page-flags.h>
+#include <linux/srcu.h>
 
 #include <asm/reg.h>
 #include <asm/cputable.h>
@@ -366,13 +367,16 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 	unsigned long req = kvmppc_get_gpr(vcpu, 3);
 	unsigned long target, ret = H_SUCCESS;
 	struct kvm_vcpu *tvcpu;
+	int idx;
 
 	switch (req) {
 	case H_ENTER:
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
 		ret = kvmppc_virtmode_h_enter(vcpu, kvmppc_get_gpr(vcpu, 4),
 					      kvmppc_get_gpr(vcpu, 5),
 					      kvmppc_get_gpr(vcpu, 6),
 					      kvmppc_get_gpr(vcpu, 7));
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
 		break;
 	case H_CEDE:
 		break;
@@ -411,6 +415,7 @@ static int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			      struct task_struct *tsk)
 {
 	int r = RESUME_HOST;
+	int srcu_idx;
 
 	vcpu->stat.sum_exits++;
 
@@ -470,12 +475,16 @@ static int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	 * have been handled already.
 	 */
 	case BOOK3S_INTERRUPT_H_DATA_STORAGE:
+		srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 		r = kvmppc_book3s_hv_page_fault(run, vcpu,
 				vcpu->arch.fault_dar, vcpu->arch.fault_dsisr);
+		srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
 		break;
 	case BOOK3S_INTERRUPT_H_INST_STORAGE:
+		srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 		r = kvmppc_book3s_hv_page_fault(run, vcpu,
 				kvmppc_get_pc(vcpu), 0);
+		srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
 		break;
 	/*
 	 * This occurs if the guest executes an illegal instruction.
@@ -820,6 +829,7 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	long ret;
 	u64 now;
 	int ptid, i, need_vpa_update;
+	int srcu_idx;
 
 	/* don't start if any threads have a signal pending */
 	need_vpa_update = 0;
@@ -898,6 +908,9 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	spin_unlock(&vc->lock);
 
 	kvm_guest_enter();
+
+	srcu_idx = srcu_read_lock(&vcpu0->kvm->srcu);
+
 	__kvmppc_vcore_entry(NULL, vcpu0);
 	for (i = 0; i < threads_per_core; ++i)
 		kvmppc_release_hwthread(vc->pcpu + i);
@@ -913,6 +926,8 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	vc->vcore_state = VCORE_EXITING;
 	spin_unlock(&vc->lock);
 
+	srcu_read_unlock(&vcpu0->kvm->srcu, srcu_idx);
+
 	/* make sure updates to secondary vcpu structs are visible now */
 	smp_mb();
 	kvm_guest_exit();
@@ -1362,6 +1377,7 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
 	unsigned long rmls;
 	unsigned long *physp;
 	unsigned long i, npages;
+	int srcu_idx;
 
 	mutex_lock(&kvm->lock);
 	if (kvm->arch.rma_setup_done)
@@ -1377,12 +1393,13 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
 	}
 
 	/* Look up the memslot for guest physical address 0 */
+	srcu_idx = srcu_read_lock(&kvm->srcu);
 	memslot = gfn_to_memslot(kvm, 0);
 
 	/* We must have some memory at 0 by now */
 	err = -EINVAL;
 	if (!memslot || (memslot->flags & KVM_MEMSLOT_INVALID))
-		goto out;
+		goto out_srcu;
 
 	/* Look up the VMA for the start of this memory slot */
 	hva = memslot->userspace_addr;
@@ -1406,14 +1423,14 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
 		err = -EPERM;
 		if (cpu_has_feature(CPU_FTR_ARCH_201)) {
 			pr_err("KVM: CPU requires an RMO\n");
-			goto out;
+			goto out_srcu;
 		}
 
 		/* We can handle 4k, 64k or 16M pages in the VRMA */
 		err = -EINVAL;
 		if (!(psize == 0x1000 || psize == 0x10000 ||
 		      psize == 0x1000000))
-			goto out;
+			goto out_srcu;
 
 		/* Update VRMASD field in the LPCR */
 		senc = slb_pgsize_encoding(psize);
@@ -1436,7 +1453,7 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
 		err = -EINVAL;
 		if (rmls < 0) {
 			pr_err("KVM: Can't use RMA of 0x%lx bytes\n", rma_size);
-			goto out;
+			goto out_srcu;
 		}
 		atomic_inc(&ri->use_count);
 		kvm->arch.rma = ri;
@@ -1476,6 +1493,8 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
 	smp_wmb();
 	kvm->arch.rma_setup_done = 1;
 	err = 0;
+ out_srcu:
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
  out:
 	mutex_unlock(&kvm->lock);
 	return err;