From 75549de770df470b024c92ff093009c6987b40fd Mon Sep 17 00:00:00 2001
From: Colin Percival <cperciva@FreeBSD.org>
Date: Wed, 2 Nov 2022 18:55:12 -0700
Subject: [PATCH] vtblk: Fix dumping

Now that vtblk uses busdma, it keeps important information inside its
request structures.  The functions used for kernel dumps synthesize
their own request structures rather than using structures initialized
with the necessary bits for busdma.

Add busdma-bypass paths.  Since dumping writes contiguous blocks of
physical memory, vtblk doesn't need busdma in that case.

Reported by:	glebius
Tested by:	glebius
Differential Revision:	https://reviews.freebsd.org/D37243
---
 sys/dev/virtio/block/virtio_blk.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/sys/dev/virtio/block/virtio_blk.c b/sys/dev/virtio/block/virtio_blk.c
index b3b3a6dd1ae..41229bb6da2 100644
--- a/sys/dev/virtio/block/virtio_blk.c
+++ b/sys/dev/virtio/block/virtio_blk.c
@@ -992,9 +992,12 @@ vtblk_request_execute(struct vtblk_request *req, int flags)
 
 	/*
 	 * Call via bus_dmamap_load_bio or directly depending on whether we
-	 * have a buffer we need to map.
+	 * have a buffer we need to map.  If we don't have a busdma map,
+	 * try to perform the I/O directly and hope that it works (this will
+	 * happen when dumping).
 	 */
-	if (bp->bio_cmd == BIO_READ || bp->bio_cmd == BIO_WRITE) {
+	if ((req->vbr_mapp != NULL) &&
+	    (bp->bio_cmd == BIO_READ || bp->bio_cmd == BIO_WRITE)) {
 		error = bus_dmamap_load_bio(sc->vtblk_dmat, req->vbr_mapp,
 		    req->vbr_bp, vtblk_request_execute_cb, req, flags);
 		if (error == EINPROGRESS) {
@@ -1080,6 +1083,15 @@ vtblk_request_execute_cb(void * callback_arg, bus_dma_segment_t * segs,
 			}
 		}
 
+		/* Special handling for dump, which bypasses busdma. */
+		if (req->vbr_mapp == NULL) {
+			error = sglist_append_bio(sg, bp);
+			if (error || sg->sg_nseg == sg->sg_maxseg) {
+				panic("%s: bio %p data buffer too big %d",
+				    __func__, bp, error);
+			}
+		}
+
 		/* BIO_READ means the host writes into our buffer. */
 		if (bp->bio_cmd == BIO_READ)
 			writable = sg->sg_nseg - 1;
@@ -1130,7 +1142,7 @@ vtblk_request_execute_cb(void * callback_arg, bus_dma_segment_t * segs,
 		virtqueue_notify(vq);
 
 out:
-	if (error)
+	if (error && (req->vbr_mapp != NULL))
 		bus_dmamap_unload(sc->vtblk_dmat, req->vbr_mapp);
 out1:
 	if (error && req->vbr_requeue_on_error)
@@ -1505,6 +1517,7 @@ vtblk_dump_write(struct vtblk_softc *sc, void *virtual, off_t offset,
 	struct vtblk_request *req;
 
 	req = &sc->vtblk_dump_request;
+	req->vbr_sc = sc;
 	req->vbr_ack = -1;
 	req->vbr_hdr.type = vtblk_gtoh32(sc, VIRTIO_BLK_T_OUT);
 	req->vbr_hdr.ioprio = vtblk_gtoh32(sc, 1);
@@ -1527,6 +1540,7 @@ vtblk_dump_flush(struct vtblk_softc *sc)
 	struct vtblk_request *req;
 
 	req = &sc->vtblk_dump_request;
+	req->vbr_sc = sc;
 	req->vbr_ack = -1;
 	req->vbr_hdr.type = vtblk_gtoh32(sc, VIRTIO_BLK_T_FLUSH);
 	req->vbr_hdr.ioprio = vtblk_gtoh32(sc, 1);