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Index: usr.sbin/bhyve/block_if.h
===================================================================
--- usr.sbin/bhyve/block_if.h
+++ usr.sbin/bhyve/block_if.h
@@ -41,7 +41,13 @@
#include <sys/uio.h>
#include <sys/unistd.h>
-#define BLOCKIF_IOV_MAX 33 /* not practical to be IOV_MAX */
+/*
+ * BLOCKIF_IOV_MAX is the maximum number of scatter/gather entries in
+ * a single request. BLOCKIF_RING_MAX is the maxmimum number of
+ * pending requests that can be queued.
+ */
+#define BLOCKIF_IOV_MAX 128 /* not practical to be IOV_MAX */
+#define BLOCKIF_RING_MAX 128
struct blockif_req {
int br_iovcnt;
Index: usr.sbin/bhyve/block_if.c
===================================================================
--- usr.sbin/bhyve/block_if.c
+++ usr.sbin/bhyve/block_if.c
@@ -65,7 +65,7 @@
#define BLOCKIF_SIG 0xb109b109
#define BLOCKIF_NUMTHR 8
-#define BLOCKIF_MAXREQ (64 + BLOCKIF_NUMTHR)
+#define BLOCKIF_MAXREQ (BLOCKIF_RING_MAX + BLOCKIF_NUMTHR)
enum blockop {
BOP_READ,
Index: usr.sbin/bhyve/pci_virtio_block.c
===================================================================
--- usr.sbin/bhyve/pci_virtio_block.c
+++ usr.sbin/bhyve/pci_virtio_block.c
@@ -3,6 +3,7 @@
*
* Copyright (c) 2011 NetApp, Inc.
* All rights reserved.
+ * Copyright (c) 2019 Joyent, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
@@ -55,8 +56,10 @@
#include "virtio.h"
#include "block_if.h"
-#define VTBLK_RINGSZ 64
+#define VTBLK_RINGSZ 128
+_Static_assert(VTBLK_RINGSZ <= BLOCKIF_RING_MAX, "Each ring entry must be able to queue a request");
+
#define VTBLK_S_OK 0
#define VTBLK_S_IOERR 1
#define VTBLK_S_UNSUPP 2
@@ -351,7 +354,15 @@
/* setup virtio block config space */
sc->vbsc_cfg.vbc_capacity = size / DEV_BSIZE; /* 512-byte units */
sc->vbsc_cfg.vbc_size_max = 0; /* not negotiated */
- sc->vbsc_cfg.vbc_seg_max = BLOCKIF_IOV_MAX;
+
+ /*
+ * If Linux is presented with a seg_max greater than the virtio queue
+ * size, it can stumble into situations where it violates its own
+ * invariants and panics. For safety, we keep seg_max clamped, paying
+ * heed to the two extra descriptors needed for the header and status
+ * of a request.
+ */
+ sc->vbsc_cfg.vbc_seg_max = MIN(VTBLK_RINGSZ - 2, BLOCKIF_IOV_MAX);
sc->vbsc_cfg.vbc_geometry.cylinders = 0; /* no geometry */
sc->vbsc_cfg.vbc_geometry.heads = 0;
sc->vbsc_cfg.vbc_geometry.sectors = 0;

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