vhost-scsi: reject feature changes after endpoint

vhost_scsi_setup_vq_cmds() runs from VHOST_SCSI_SET_ENDPOINT and allocates
each command's protection scatterlist array (prot_sgl) according to the
acknowledged VIRTIO_SCSI_F_T10_PI bit.  The command pools are not rebuilt
when VHOST_SET_FEATURES changes that bit later.

Although virtio feature bits must not change after feature negotiation,
vhost_scsi_set_features() currently accepts such a request after the
endpoint is active and updates acked_features.  Enabling T10-PI after
endpoint setup therefore leaves prot_sgl NULL while the I/O path follows
the new feature bit.

For a 129-page protection payload, vhost_scsi_mapal() passes the missing
first chunk to sg_alloc_table_chained():

  sg_alloc_table_chained(table, 129, first_chunk=NULL,
                         nents_first_chunk=inline_sg_cnt)

sg_pool_index() then hits:

  BUG_ON(nents > SG_CHUNK_SIZE);   /* 129 > 128 */

The kernel reported the following call trace and register state:

  Call Trace:
   <TASK>
   ? __sg_alloc_table+0x1d8/0x250
   ? __pfx_vhost_run_work_list+0x10/0x10 [vhost]
   sg_alloc_table_chained+0x59/0xf0
   ? __pfx_sg_pool_alloc+0x10/0x10
   ? vhost_scsi_calc_sgls.constprop.0+0x43/0x60 [vhost_scsi]
   vhost_scsi_handle_vq+0xf02/0x1700 [vhost_scsi]
   ? __pfx_vhost_scsi_handle_vq+0x10/0x10 [vhost_scsi]
   vhost_scsi_handle_kick+0x37/0x50 [vhost_scsi]
   vhost_run_work_list+0x8e/0xd0 [vhost]
   vhost_task_fn+0xe1/0x210
   ret_from_fork+0x348/0x540
   </TASK>

  RIP: 0010:0x4
  CR2 = 0x4
  RSP: 0018:ffffc90000dbf940 EFLAGS: 00010202
  RAX: ffffffff82396810 RBX: ffff88811dc28b80 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000081

VHOST_F_LOG_ALL is a vhost-specific runtime feature and remains the only
exception.

Reject changes to any feature other than VHOST_F_LOG_ALL while the
endpoint is active.  This preserves the existing runtime log toggle while
preventing feature-dependent command resources and data-path state from
becoming inconsistent.  Userspace must clear the endpoint before changing
any other negotiated feature and set the endpoint up again afterward.

Fixes: bf2d650391be ("vhost-scsi: Allocate T10 PI structs only when enabled")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20260726144314.1652934-1-physicalmtea@gmail.com>

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index aae1164e1ca9e333d21db6b4acc6e6c6e26f25ed..7a1f39a327da63921fb68777368eaeb82aefb89a 100644 (file)
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -2227,6 +2227,7 @@ static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
 {
        struct vhost_virtqueue *vq;
        bool is_log, was_log;
+       u64 old_features;
        int i;
 
        if (features & ~VHOST_SCSI_FEATURES)
@@ -2242,6 +2243,14 @@ static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
        if (!vs->dev.nvqs)
                goto out;
 
+       old_features = vs->vqs[0].vq.acked_features;
+       if (vs->vs_tpg &&
+           ((features ^ old_features) &
+            ~(1ULL << VHOST_F_LOG_ALL))) {
+               mutex_unlock(&vs->dev.mutex);
+               return -EBUSY;
+       }
+
        is_log = features & (1 << VHOST_F_LOG_ALL);
        /*
         * All VQs should have same feature.