KVM: kvm-io: support cookies

Add new functions kvm_io_bus_{read,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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 92 insertions, 16 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1580dd4ace4e..71960fb03c2a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2863,13 +2863,33 @@ static int kvm_io_bus_get_first_dev(struct kvm_io_bus *bus,
         return off;
 }
 
+static int __kvm_io_bus_write(struct kvm_io_bus *bus,
+                              struct kvm_io_range *range, const void *val)
+{
+        int idx;
+
+        idx = kvm_io_bus_get_first_dev(bus, range->addr, range->len);
+        if (idx < 0)
+                return -EOPNOTSUPP;
+
+        while (idx < bus->dev_count &&
+                kvm_io_bus_sort_cmp(range, &bus->range[idx]) == 0) {
+                if (!kvm_iodevice_write(bus->range[idx].dev, range->addr,
+                                        range->len, val))
+                        return idx;
+                idx++;
+        }
+
+        return -EOPNOTSUPP;
+}
+
 /* kvm_io_bus_write - called under kvm->slots_lock */
 int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
                      int len, const void *val)
 {
-        int idx;
         struct kvm_io_bus *bus;
         struct kvm_io_range range;
+        int r;
 
         range = (struct kvm_io_range) {
                 .addr = addr,
@@ -2877,14 +2897,52 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
         };
 
         bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
-        idx = kvm_io_bus_get_first_dev(bus, addr, len);
+        r = __kvm_io_bus_write(bus, &range, val);
+        return r < 0 ? r : 0;
+}
+
+/* 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)
+{
+        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 cookie;
+
+        /*
+         * cookie contained garbage; fall back to search and return the
+         * correct cookie value.
+         */
+        return __kvm_io_bus_write(bus, &range, val);
+}
+
+static int __kvm_io_bus_read(struct kvm_io_bus *bus, struct kvm_io_range *range,
+                             void *val)
+{
+        int idx;
+
+        idx = kvm_io_bus_get_first_dev(bus, range->addr, range->len);
         if (idx < 0)
                 return -EOPNOTSUPP;
 
         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))
-                        return 0;
+                kvm_io_bus_sort_cmp(range, &bus->range[idx]) == 0) {
+                if (!kvm_iodevice_read(bus->range[idx].dev, range->addr,
+                                       range->len, val))
+                        return idx;
                 idx++;
         }
 
@@ -2895,9 +2953,9 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
                     int len, void *val)
 {
-        int idx;
         struct kvm_io_bus *bus;
         struct kvm_io_range range;
+        int r;
 
         range = (struct kvm_io_range) {
                 .addr = addr,
@@ -2905,18 +2963,36 @@ int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
         };
 
         bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
-        idx = kvm_io_bus_get_first_dev(bus, addr, len);
-        if (idx < 0)
-                return -EOPNOTSUPP;
+        r = __kvm_io_bus_read(bus, &range, val);
+        return r < 0 ? r : 0;
+}
 
-        while (idx < bus->dev_count &&
-                kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
-                if (!kvm_iodevice_read(bus->range[idx].dev, addr, len, val))
-                        return 0;
-                idx++;
-        }
+/* kvm_io_bus_read_cookie - called under kvm->slots_lock */
+int kvm_io_bus_read_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
+                           int len, void *val, long cookie)
+{
+        struct kvm_io_bus *bus;
+        struct kvm_io_range range;
 
-        return -EOPNOTSUPP;
+        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_read(bus->range[cookie].dev, addr, len,
+                                       val))
+                        return cookie;
+
+        /*
+         * cookie contained garbage; fall back to search and return the
+         * correct cookie value.
+         */
+        return __kvm_io_bus_read(bus, &range, val);
 }
 
 /* Caller must hold slots_lock. */