[PATCH 1/2] KVM: kvm-io: support cookies

[Cornelia Huck <cornelia.huck@de.ibm.com>]

Add a new function kvm_io_bus_write_cookie() that allows users of the
kvm io infrastructure to use a cookie value to speed up lookup of a
device on an io bus.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e3aae6d..2d298fc 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -159,6 +159,8 @@ enum kvm_bus {
 
 int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 		     int len, const void *val);
+int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
+			    int len, const void *val, long *cookie);
 int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int len,
 		    void *val);
 int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1580dd4..222475a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2891,6 +2891,50 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 	return -EOPNOTSUPP;
 }
 
+/* kvm_io_bus_write_cookie - called under kvm->slots_lock */
+int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
+			    int len, const void *val, long *cookie)
+{
+	int idx, ret = -EOPNOTSUPP;
+	struct kvm_io_bus *bus;
+	struct kvm_io_range range;
+
+	range = (struct kvm_io_range) {
+		.addr = addr,
+		.len = len,
+	};
+
+	bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
+
+	/* First try the device referenced by *cookie. */
+	if ((*cookie >= 0) && (*cookie < bus->dev_count) &&
+	    (kvm_io_bus_sort_cmp(&range, &bus->range[*cookie]) == 0))
+		if (!kvm_iodevice_write(bus->range[*cookie].dev, addr, len,
+					val))
+			return 0;
+
+	/*
+	 * *cookie contained garbage; fall back to search and return the
+	 * correct value in *cookie.
+	 */
+	idx = kvm_io_bus_get_first_dev(bus, addr, len);
+	if (idx < 0)
+		goto out;
+
+	while (idx < bus->dev_count &&
+		kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
+		if (!kvm_iodevice_write(bus->range[idx].dev, addr, len, val)) {
+			ret = 0;
+			goto out;
+		}
+		idx++;
+	}
+	idx = -ENOENT;
+out:
+	*cookie = idx;
+	return ret;
+}
+
 /* kvm_io_bus_read - called under kvm->slots_lock */
 int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 		    int len, void *val)
-- 
1.8.2.2