kvm: Introduce basic MSI support for in-kernel irqchips

This patch basically adds kvm_irqchip_send_msi, a service for sending
arbitrary MSI messages to KVM's in-kernel irqchip models.

As the original KVM API requires us to establish a static route from a
pseudo GSI to the target MSI message and inject the MSI via toggling
that virtual IRQ, we need to play some tricks to make this interface
transparent. We create those routes on demand and keep them in a hash
table. Succeeding messages can then search for an existing route in the
table first and reuse it whenever possible. If we should run out of
limited GSIs, we simply flush the table and rebuild it as messages are
sent.

This approach is rather simple and could be optimized further. However,
latest kernels contains a more efficient MSI injection interface that
will obsolete the GSI-based dynamic injection.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

2 files changed, 139 insertions, 1 deletions

diff --git a/kvm-all.c b/kvm-all.c
index 2d82d54..ff0534b 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -24,6 +24,7 @@
 #include "qemu-barrier.h"
 #include "sysemu.h"
 #include "hw/hw.h"
+#include "hw/msi.h"
 #include "gdbstub.h"
 #include "kvm.h"
 #include "bswap.h"
@@ -48,6 +49,8 @@
     do { } while (0)
 #endif
 
+#define KVM_MSI_HASHTAB_SIZE    256
+
 typedef struct KVMSlot
 {
     target_phys_addr_t start_addr;
@@ -59,6 +62,11 @@ typedef struct KVMSlot
 
 typedef struct kvm_dirty_log KVMDirtyLog;
 
+typedef struct KVMMSIRoute {
+    struct kvm_irq_routing_entry kroute;
+    QTAILQ_ENTRY(KVMMSIRoute) entry;
+} KVMMSIRoute;
+
 struct KVMState
 {
     KVMSlot slots[32];
@@ -87,6 +95,7 @@ struct KVMState
     int nr_allocated_irq_routes;
     uint32_t *used_gsi_bitmap;
     unsigned int gsi_count;
+    QTAILQ_HEAD(msi_hashtab, KVMMSIRoute) msi_hashtab[KVM_MSI_HASHTAB_SIZE];
 #endif
 };
 
@@ -862,9 +871,14 @@ static void set_gsi(KVMState *s, unsigned int gsi)
     s->used_gsi_bitmap[gsi / 32] |= 1U << (gsi % 32);
 }
 
+static void clear_gsi(KVMState *s, unsigned int gsi)
+{
+    s->used_gsi_bitmap[gsi / 32] &= ~(1U << (gsi % 32));
+}
+
 static void kvm_init_irq_routing(KVMState *s)
 {
-    int gsi_count;
+    int gsi_count, i;
 
     gsi_count = kvm_check_extension(s, KVM_CAP_IRQ_ROUTING);
     if (gsi_count > 0) {
@@ -884,6 +898,10 @@ static void kvm_init_irq_routing(KVMState *s)
     s->irq_routes = g_malloc0(sizeof(*s->irq_routes));
     s->nr_allocated_irq_routes = 0;
 
+    for (i = 0; i < KVM_MSI_HASHTAB_SIZE; i++) {
+        QTAILQ_INIT(&s->msi_hashtab[i]);
+    }
+
     kvm_arch_init_irq_routing(s);
 }
 
@@ -934,11 +952,130 @@ int kvm_irqchip_commit_routes(KVMState *s)
     return kvm_vm_ioctl(s, KVM_SET_GSI_ROUTING, s->irq_routes);
 }
 
+static void kvm_irqchip_release_virq(KVMState *s, int virq)
+{
+    struct kvm_irq_routing_entry *e;
+    int i;
+
+    for (i = 0; i < s->irq_routes->nr; i++) {
+        e = &s->irq_routes->entries[i];
+        if (e->gsi == virq) {
+            s->irq_routes->nr--;
+            *e = s->irq_routes->entries[s->irq_routes->nr];
+        }
+    }
+    clear_gsi(s, virq);
+}
+
+static unsigned int kvm_hash_msi(uint32_t data)
+{
+    /* This is optimized for IA32 MSI layout. However, no other arch shall
+     * repeat the mistake of not providing a direct MSI injection API. */
+    return data & 0xff;
+}
+
+static void kvm_flush_dynamic_msi_routes(KVMState *s)
+{
+    KVMMSIRoute *route, *next;
+    unsigned int hash;
+
+    for (hash = 0; hash < KVM_MSI_HASHTAB_SIZE; hash++) {
+        QTAILQ_FOREACH_SAFE(route, &s->msi_hashtab[hash], entry, next) {
+            kvm_irqchip_release_virq(s, route->kroute.gsi);
+            QTAILQ_REMOVE(&s->msi_hashtab[hash], route, entry);
+            g_free(route);
+        }
+    }
+}
+
+static int kvm_irqchip_get_virq(KVMState *s)
+{
+    uint32_t *word = s->used_gsi_bitmap;
+    int max_words = ALIGN(s->gsi_count, 32) / 32;
+    int i, bit;
+    bool retry = true;
+
+again:
+    /* Return the lowest unused GSI in the bitmap */
+    for (i = 0; i < max_words; i++) {
+        bit = ffs(~word[i]);
+        if (!bit) {
+            continue;
+        }
+
+        return bit - 1 + i * 32;
+    }
+    if (retry) {
+        retry = false;
+        kvm_flush_dynamic_msi_routes(s);
+        goto again;
+    }
+    return -ENOSPC;
+
+}
+
+static KVMMSIRoute *kvm_lookup_msi_route(KVMState *s, MSIMessage msg)
+{
+    unsigned int hash = kvm_hash_msi(msg.data);
+    KVMMSIRoute *route;
+
+    QTAILQ_FOREACH(route, &s->msi_hashtab[hash], entry) {
+        if (route->kroute.u.msi.address_lo == (uint32_t)msg.address &&
+            route->kroute.u.msi.address_hi == (msg.address >> 32) &&
+            route->kroute.u.msi.data == msg.data) {
+            return route;
+        }
+    }
+    return NULL;
+}
+
+int kvm_irqchip_send_msi(KVMState *s, MSIMessage msg)
+{
+    KVMMSIRoute *route;
+
+    route = kvm_lookup_msi_route(s, msg);
+    if (!route) {
+        int virq, ret;
+
+        virq = kvm_irqchip_get_virq(s);
+        if (virq < 0) {
+            return virq;
+        }
+
+        route = g_malloc(sizeof(KVMMSIRoute));
+        route->kroute.gsi = virq;
+        route->kroute.type = KVM_IRQ_ROUTING_MSI;
+        route->kroute.flags = 0;
+        route->kroute.u.msi.address_lo = (uint32_t)msg.address;
+        route->kroute.u.msi.address_hi = msg.address >> 32;
+        route->kroute.u.msi.data = msg.data;
+
+        kvm_add_routing_entry(s, &route->kroute);
+
+        QTAILQ_INSERT_TAIL(&s->msi_hashtab[kvm_hash_msi(msg.data)], route,
+                           entry);
+
+        ret = kvm_irqchip_commit_routes(s);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    assert(route->kroute.type == KVM_IRQ_ROUTING_MSI);
+
+    return kvm_irqchip_set_irq(s, route->kroute.gsi, 1);
+}
+
 #else /* !KVM_CAP_IRQ_ROUTING */
 
 static void kvm_init_irq_routing(KVMState *s)
 {
 }
+
+int kvm_irqchip_send_msi(KVMState *s, MSIMessage msg)
+{
+    abort();
+}
 #endif /* !KVM_CAP_IRQ_ROUTING */
 
 static int kvm_irqchip_create(KVMState *s)
diff --git a/kvm.h b/kvm.h
index 4ccae8c..7857dbf 100644
--- a/kvm.h
+++ b/kvm.h
@@ -132,6 +132,7 @@ int kvm_arch_on_sigbus(int code, void *addr);
 void kvm_arch_init_irq_routing(KVMState *s);
 
 int kvm_irqchip_set_irq(KVMState *s, int irq, int level);
+int kvm_irqchip_send_msi(KVMState *s, MSIMessage msg);
 
 void kvm_irqchip_add_route(KVMState *s, int gsi, int irqchip, int pin);
 int kvm_irqchip_commit_routes(KVMState *s);