KVM: PPC: Accelerate H_PUT_TCE by implementing it in real mode

This improves I/O performance for guests using the PAPR
paravirtualization interface by making the H_PUT_TCE hcall faster, by
implementing it in real mode.  H_PUT_TCE is used for updating virtual
IOMMU tables, and is used both for virtual I/O and for real I/O in the
PAPR interface.

Since this moves the IOMMU tables into the kernel, we define a new
KVM_CREATE_SPAPR_TCE ioctl to allow qemu to create the tables.  The
ioctl returns a file descriptor which can be used to mmap the newly
created table.  The qemu driver models use them in the same way as
userspace managed tables, but they can be updated directly by the
guest with a real-mode H_PUT_TCE implementation, reducing the number
of host/guest context switches during guest IO.

There are certain circumstances where it is useful for userland qemu
to write to the TCE table even if the kernel H_PUT_TCE path is used
most of the time.  Specifically, allowing this will avoid awkwardness
when we need to reset the table.  More importantly, we will in the
future need to write the table in order to restore its state after a
checkpoint resume or migration.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 6fc9ee499b6..c78ceb9d560 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -203,6 +203,11 @@ int kvm_dev_ioctl_check_extension(long ext)
 		r = KVM_COALESCED_MMIO_PAGE_OFFSET;
 		break;
 #endif
+#ifdef CONFIG_KVM_BOOK3S_64_HV
+	case KVM_CAP_SPAPR_TCE:
+		r = 1;
+		break;
+#endif
 	default:
 		r = 0;
 		break;
@@ -653,6 +658,19 @@ long kvm_arch_vm_ioctl(struct file *filp,
 
 		break;
 	}
+#ifdef CONFIG_KVM_BOOK3S_64_HV
+	case KVM_CREATE_SPAPR_TCE: {
+		struct kvm_create_spapr_tce create_tce;
+		struct kvm *kvm = filp->private_data;
+
+		r = -EFAULT;
+		if (copy_from_user(&create_tce, argp, sizeof(create_tce)))
+			goto out;
+		r = kvm_vm_ioctl_create_spapr_tce(kvm, &create_tce);
+		goto out;
+	}
+#endif /* CONFIG_KVM_BOOK3S_64_HV */
+
 	default:
 		r = -ENOTTY;
 	}