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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 8/25/21 10:09 PM, Philippe Mathieu-Daudé wrote:
> 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);
>  }

Self-NAck.

While the previous part could be OK, what follows is crap (checking
avail instead of used) so please disregard this patch.

> @@ -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;
>