[RFC PATCH] hw/virtio: Do not access vring cache if queue is not ready

[Philippe Mathieu-Daudé]

Do not intent to access the vring MemoryRegion cache if
the queue is not ready (no vring available).

This fixes issue #301:

  qemu-system-i386: include/exec/memory_ldst_cached.h.inc:77: void 
address_space_stw_le_cached(MemoryRegionCache *, hwaddr, uint16_t, MemTxAttrs, 
MemTxResult *):
  Assertion `addr < cache->len && 2 <= cache->len - addr' failed.
  Thread 1 "qemu-system-i38" received signal SIGABRT, Aborted.
  (gdb) bt
  #1  0x00007ffff4d1a8a4 in abort () at /lib64/libc.so.6
  #4  0x0000555558f2a122 in address_space_stw_le_cached (cache=0x61300010bb70, 
addr=516, val=0, attrs=..., result=0x0) at 
include/exec/memory_ldst_cached.h.inc:77
  #5  0x0000555558f2964c in stw_le_phys_cached (cache=0x61300010bb70, addr=516, 
val=0) at include/exec/memory_ldst_phys.h.inc:109
  #6  0x0000555558f28da8 in virtio_stw_phys_cached (vdev=0x62d00004e680, 
cache=0x61300010bb70, pa=516, value=0) at include/hw/virtio/virtio-access.h:196
  #7  0x0000555558f287dc in vring_set_avail_event (vq=0x7fff5d23e800, val=0) at 
hw/virtio/virtio.c:428
  #8  0x0000555558efabb7 in virtio_queue_split_set_notification 
(vq=0x7fff5d23e800, enable=1) at hw/virtio/virtio.c:437
  #9  0x0000555558ef9f3c in virtio_queue_set_notification (vq=0x7fff5d23e800, 
enable=1) at hw/virtio/virtio.c:498
  #10 0x0000555558c94786 in virtio_blk_handle_vq (s=0x62d00004e680, 
vq=0x7fff5d23e800) at hw/block/virtio-blk.c:795
  #11 0x0000555558cb96c2 in virtio_blk_data_plane_handle_output 
(vdev=0x62d00004e680, vq=0x7fff5d23e800) at hw/block/dataplane/virtio-blk.c:165
  #12 0x0000555558f35937 in virtio_queue_notify_aio_vq (vq=0x7fff5d23e800) at 
hw/virtio/virtio.c:2323
  #13 0x0000555558f264b3 in virtio_queue_host_notifier_aio_read 
(n=0x7fff5d23e87c) at hw/virtio/virtio.c:3532
  #14 0x0000555559a9cd3e in aio_dispatch_handler (ctx=0x613000063000, 
node=0x60d000008f40) at util/aio-posix.c:329
  #15 0x0000555559a963ae in aio_dispatch_handlers (ctx=0x613000063000) at 
util/aio-posix.c:372
  #16 0x0000555559a95f82 in aio_dispatch (ctx=0x613000063000) at 
util/aio-posix.c:382

and  #302:

  qemu-system-i386: include/exec/memory_ldst_cached.h.inc:30: uint16_t 
address_space_lduw_le_cached(MemoryRegionCache *, hwaddr, MemTxAttrs, 
MemTxResult *):
  Assertion `addr < cache->len && 2 <= cache->len - addr' failed.
  Thread 1 "qemu-system-i38" received signal SIGABRT, Aborted.
  0x00007ffff4d312a2 in raise () from /lib64/libc.so.6
  (gdb) bt
  #1  0x00007ffff4d1a8a4 in abort () at /lib64/libc.so.6
  #4  0x0000555558f2b8ec in address_space_lduw_le_cached (cache=0x61300010a7c0, 
addr=134, attrs=..., result=0x0) at include/exec/memory_ldst_cached.h.inc:30
  #5  0x0000555558f2ac6b in lduw_le_phys_cached (cache=0x61300010a7c0, 
addr=134) at include/exec/memory_ldst_phys.h.inc:67
  #6  0x0000555558f2a3cd in virtio_lduw_phys_cached (vdev=0x62d00003a680, 
cache=0x61300010a7c0, pa=134) at include/hw/virtio/virtio-access.h:166
  #7  0x0000555558f300ea in vring_avail_ring (vq=0x7fffdd55d8a0, i=65) at 
hw/virtio/virtio.c:326
  #8  0x0000555558f33b10 in vring_get_used_event (vq=0x7fffdd55d8a0) at 
hw/virtio/virtio.c:332
  #9  0x0000555558f33677 in virtio_split_should_notify (vdev=0x62d00003a680, 
vq=0x7fffdd55d8a0) at hw/virtio/virtio.c:2471
  #10 0x0000555558f1859f in virtio_should_notify (vdev=0x62d00003a680, 
vq=0x7fffdd55d8a0) at hw/virtio/virtio.c:2523
  #11 0x0000555558f188cc in virtio_notify (vdev=0x62d00003a680, 
vq=0x7fffdd55d8a0) at hw/virtio/virtio.c:2565
  #12 0x0000555557c2bd52 in virtio_input_handle_sts (vdev=0x62d00003a680, 
vq=0x7fffdd55d8a0) at hw/input/virtio-input.c:100
  #13 0x0000555558f16df7 in virtio_queue_notify (vdev=0x62d00003a680, n=1) at 
hw/virtio/virtio.c:2363
  #14 0x00005555583f45c0 in virtio_pci_notify_write (opaque=0x62d000032400, 
addr=7, val=0, size=1) at hw/virtio/virtio-pci.c:1369
  #15 0x0000555558b80b04 in memory_region_write_accessor (mr=0x62d000033190, 
addr=7, value=0x7fffffff8eb0, size=1, shift=0, mask=255, attrs=...) at 
softmmu/memory.c:492

Reported-by: Cheolwoo Myung <cwmyung@snu.ac.kr>
Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/301
BugLink: https://bugs.launchpad.net/qemu/+bug/1910941
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/302
BugLink: https://bugs.launchpad.net/qemu/+bug/1913510
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
Could be more readable to use virtio_queue_ready()

RFC because I have no clue about this hot path code,
I simply looked at the backtraces.
---
 hw/virtio/virtio.c | 82 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 66 insertions(+), 16 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 874377f37a7..be1ec9e05ef 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -289,26 +289,38 @@ static VRingMemoryRegionCaches 
*vring_get_region_caches(struct VirtQueue *vq)
 /* Called within rcu_read_lock().  */
 static inline uint16_t vring_avail_flags(VirtQueue *vq)
 {
-    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
-    hwaddr pa = offsetof(VRingAvail, flags);
+    VRingMemoryRegionCaches *caches;
+    hwaddr pa;
 
+    if (unlikely(!vq->vring.avail)) {
+        return 0;
+    }
+
+    caches = vring_get_region_caches(vq);
     if (!caches) {
         return 0;
     }
 
+    pa = offsetof(VRingAvail, flags);
     return virtio_lduw_phys_cached(vq->vdev, &caches->avail, pa);
 }
 
 /* Called within rcu_read_lock().  */
 static inline uint16_t vring_avail_idx(VirtQueue *vq)
 {
-    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
-    hwaddr pa = offsetof(VRingAvail, idx);
+    VRingMemoryRegionCaches *caches;
+    hwaddr pa;
 
+    if (unlikely(!vq->vring.avail)) {
+        return 0;
+    }
+
+    caches = vring_get_region_caches(vq);
     if (!caches) {
         return 0;
     }
 
+    pa = offsetof(VRingAvail, idx);
     vq->shadow_avail_idx = virtio_lduw_phys_cached(vq->vdev, &caches->avail, 
pa);
     return vq->shadow_avail_idx;
 }
@@ -316,13 +328,19 @@ static inline uint16_t vring_avail_idx(VirtQueue *vq)
 /* Called within rcu_read_lock().  */
 static inline uint16_t vring_avail_ring(VirtQueue *vq, int i)
 {
-    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
-    hwaddr pa = offsetof(VRingAvail, ring[i]);
+    VRingMemoryRegionCaches *caches;
+    hwaddr pa;
 
+    if (unlikely(!vq->vring.avail)) {
+        return 0;
+    }
+
+    caches = vring_get_region_caches(vq);
     if (!caches) {
         return 0;
     }
 
+    pa = offsetof(VRingAvail, ring[i]);
     return virtio_lduw_phys_cached(vq->vdev, &caches->avail, pa);
 }
 
@@ -336,13 +354,19 @@ static inline uint16_t vring_get_used_event(VirtQueue *vq)
 static inline void vring_used_write(VirtQueue *vq, VRingUsedElem *uelem,
                                     int i)
 {
-    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
-    hwaddr pa = offsetof(VRingUsed, ring[i]);
+    VRingMemoryRegionCaches *caches;
+    hwaddr pa;
 
+    if (unlikely(!vq->vring.avail)) {
+        return;
+    }
+
+    caches = vring_get_region_caches(vq);
     if (!caches) {
         return;
     }
 
+    pa = offsetof(VRingUsed, ring[i]);
     virtio_tswap32s(vq->vdev, &uelem->id);
     virtio_tswap32s(vq->vdev, &uelem->len);
     address_space_write_cached(&caches->used, pa, uelem, 
sizeof(VRingUsedElem));
@@ -352,23 +376,35 @@ static inline void vring_used_write(VirtQueue *vq, 
VRingUsedElem *uelem,
 /* Called within rcu_read_lock().  */
 static uint16_t vring_used_idx(VirtQueue *vq)
 {
-    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
-    hwaddr pa = offsetof(VRingUsed, idx);
+    VRingMemoryRegionCaches *caches;
+    hwaddr pa;
 
+    if (unlikely(!vq->vring.avail)) {
+        return 0;
+    }
+
+    caches = vring_get_region_caches(vq);
     if (!caches) {
         return 0;
     }
 
+    pa = offsetof(VRingUsed, idx);
     return virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
 }
 
 /* Called within rcu_read_lock().  */
 static inline void vring_used_idx_set(VirtQueue *vq, uint16_t val)
 {
-    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
-    hwaddr pa = offsetof(VRingUsed, idx);
+    VRingMemoryRegionCaches *caches;
 
+    if (unlikely(!vq->vring.avail)) {
+        return;
+    }
+
+    caches = vring_get_region_caches(vq);
     if (caches) {
+        hwaddr pa = offsetof(VRingUsed, idx);
+
         virtio_stw_phys_cached(vq->vdev, &caches->used, pa, val);
         address_space_cache_invalidate(&caches->used, pa, sizeof(val));
     }
@@ -379,17 +415,22 @@ static inline void vring_used_idx_set(VirtQueue *vq, 
uint16_t val)
 /* Called within rcu_read_lock().  */
 static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask)
 {
-    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
-    VirtIODevice *vdev = vq->vdev;
-    hwaddr pa = offsetof(VRingUsed, flags);
+    VRingMemoryRegionCaches *caches;
+    hwaddr pa;
     uint16_t flags;
 
+    if (unlikely(!vq->vring.avail)) {
+        return;
+    }
+
+    caches = vring_get_region_caches(vq);
     if (!caches) {
         return;
     }
 
+    pa = offsetof(VRingUsed, flags);
     flags = virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
-    virtio_stw_phys_cached(vdev, &caches->used, pa, flags | mask);
+    virtio_stw_phys_cached(vq->vdev, &caches->used, pa, flags | mask);
     address_space_cache_invalidate(&caches->used, pa, sizeof(flags));
 }
 
@@ -401,6 +442,10 @@ static inline void vring_used_flags_unset_bit(VirtQueue 
*vq, int mask)
     hwaddr pa = offsetof(VRingUsed, flags);
     uint16_t flags;
 
+    if (unlikely(!vq->vring.avail)) {
+        return;
+    }
+
     if (!caches) {
         return;
     }
@@ -415,10 +460,15 @@ static inline void vring_set_avail_event(VirtQueue *vq, 
uint16_t val)
 {
     VRingMemoryRegionCaches *caches;
     hwaddr pa;
+
     if (!vq->notification) {
         return;
     }
 
+    if (unlikely(!vq->vring.avail)) {
+        return;
+    }
+
     caches = vring_get_region_caches(vq);
     if (!caches) {
         return;
-- 
2.31.1