3 files changed, 27 insertions, 1 deletions
diff --git a/usr/src/cmd/bhyve/block_if.c b/usr/src/cmd/bhyve/block_if.c
index c8ec96690c..010f010c38 100644
--- a/usr/src/cmd/bhyve/block_if.c
+++ b/usr/src/cmd/bhyve/block_if.c
@@ -66,7 +66,12 @@ __FBSDID("$FreeBSD$");
 #define BLOCKIF_SIG	0xb109b109
 
 #define BLOCKIF_NUMTHR	8
+#ifdef __FreeBSD__
 #define BLOCKIF_MAXREQ	(64 + BLOCKIF_NUMTHR)
+#else
+/* Enlarge to keep pace with the virtio-block ring size */
+#define BLOCKIF_MAXREQ	(128 + BLOCKIF_NUMTHR)
+#endif
 
 enum blockop {
 	BOP_READ,
diff --git a/usr/src/cmd/bhyve/block_if.h b/usr/src/cmd/bhyve/block_if.h
index 930cd62e83..265048d90f 100644
--- a/usr/src/cmd/bhyve/block_if.h
+++ b/usr/src/cmd/bhyve/block_if.h
@@ -44,7 +44,12 @@
 #ifdef	__FreeBSD__
 #define BLOCKIF_IOV_MAX		33	/* not practical to be IOV_MAX */
 #else
-#define BLOCKIF_IOV_MAX		17	/* not practical to be IOV_MAX */
+/*
+ * Upstream is in the process of bumping this up to 128 for several reasons,
+ * including Windows compatibility.  For the sake of our Windows support, we
+ * will use the higher value now.
+ */
+#define	BLOCKIF_IOV_MAX		128
 #endif
 
 struct blockif_req {
diff --git a/usr/src/cmd/bhyve/pci_virtio_block.c b/usr/src/cmd/bhyve/pci_virtio_block.c
index 63f59e6468..d2f6ac7785 100644
--- a/usr/src/cmd/bhyve/pci_virtio_block.c
+++ b/usr/src/cmd/bhyve/pci_virtio_block.c
@@ -68,7 +68,12 @@ __FBSDID("$FreeBSD$");
 #include "virtio.h"
 #include "block_if.h"
 
+#ifdef __FreeBSD__
 #define VTBLK_RINGSZ	64
+#else
+/* Enlarge to match bigger BLOCKIF_IOV_MAX */
+#define VTBLK_RINGSZ	128
+#endif
 
 #define VTBLK_S_OK	0
 #define VTBLK_S_IOERR	1
@@ -376,7 +381,18 @@ pci_vtblk_init(struct vmctx *ctx, struct pci_devinst *pi, char *opts)
 	/* 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 */
+#ifdef __FreeBSD__
 	sc->vbsc_cfg.vbc_seg_max = BLOCKIF_IOV_MAX;
+#else
+	/*
+	 * 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);
+#endif
 	sc->vbsc_cfg.vbc_geometry.cylinders = 0;	/* no geometry */
 	sc->vbsc_cfg.vbc_geometry.heads = 0;
 	sc->vbsc_cfg.vbc_geometry.sectors = 0;