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From 851ffb4eea917e2708c912291dea4d133026c0ac Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Fri, 20 Nov 2015 12:16:02 -0500
Subject: [PATCH 2/3] blktap2: Use RING_COPY_REQUEST
Instead of RING_GET_REQUEST. Using a local copy of the
ring (and also with proper memory barriers) will mean
we can do not have to worry about the compiler optimizing
the code and doing a double-fetch in the shared memory space.
This is part of XSA155.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
v2: Fix compile issues with tapdisk-vbd
---
tools/blktap2/drivers/block-log.c | 3 ++-
tools/blktap2/drivers/tapdisk-vbd.c | 8 ++++----
2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/tools/blktap2/drivers/block-log.c b/tools/blktap2/drivers/block-log.c
index 5330cdc..5f3bd35 100644
--- a/tools/blktap2/drivers/block-log.c
+++ b/tools/blktap2/drivers/block-log.c
@@ -494,11 +494,12 @@ static int ctl_kick(struct tdlog_state* s, int fd)
reqstart = s->bring.req_cons;
reqend = s->sring->req_prod;
+ xen_mb();
BDPRINTF("ctl: ring kicked (start = %u, end = %u)", reqstart, reqend);
while (reqstart != reqend) {
/* XXX actually submit these! */
- memcpy(&req, RING_GET_REQUEST(&s->bring, reqstart), sizeof(req));
+ RING_COPY_REQUEST(&s->bring, reqstart, &req);
BDPRINTF("ctl: read request %"PRIu64":%u", req.sector, req.count);
s->bring.req_cons = ++reqstart;
diff --git a/tools/blktap2/drivers/tapdisk-vbd.c b/tools/blktap2/drivers/tapdisk-vbd.c
index 6d1d94a..89ef9ed 100644
--- a/tools/blktap2/drivers/tapdisk-vbd.c
+++ b/tools/blktap2/drivers/tapdisk-vbd.c
@@ -1555,7 +1555,7 @@ tapdisk_vbd_pull_ring_requests(td_vbd_t *vbd)
int idx;
RING_IDX rp, rc;
td_ring_t *ring;
- blkif_request_t *req;
+ blkif_request_t req;
td_vbd_request_t *vreq;
ring = &vbd->ring;
@@ -1566,16 +1566,16 @@ tapdisk_vbd_pull_ring_requests(td_vbd_t *vbd)
xen_rmb();
for (rc = ring->fe_ring.req_cons; rc != rp; rc++) {
- req = RING_GET_REQUEST(&ring->fe_ring, rc);
+ RING_COPY_REQUEST(&ring->fe_ring, rc, &req);
++ring->fe_ring.req_cons;
- idx = req->id;
+ idx = req.id;
vreq = &vbd->request_list[idx];
ASSERT(list_empty(&vreq->next));
ASSERT(vreq->secs_pending == 0);
- memcpy(&vreq->req, req, sizeof(blkif_request_t));
+ memcpy(&vreq->req, &req, sizeof(blkif_request_t));
vbd->received++;
vreq->vbd = vbd;
--
2.1.4
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