aboutsummaryrefslogtreecommitdiff
path: root/dma-helpers.c
diff options
context:
space:
mode:
authorPavel Dovgalyuk <pavel.dovgaluk@gmail.com>2020-06-03 13:22:02 +0300
committerKevin Wolf <kwolf@redhat.com>2020-06-17 14:53:39 +0200
commit5fb0a6b5e771b235275acc8af7da490de072917b (patch)
treeed8484daae51fb194aaa34b8dd84cd523476ca0d /dma-helpers.c
parentae0cebd71215188951902c5ccdd8685e431c286c (diff)
icount: make dma reads deterministic
Windows guest sometimes makes DMA requests with overlapping target addresses. This leads to the following structure of iov for the block driver: addr size1 addr size2 addr size3 It means that three adjacent disk blocks should be read into the same memory buffer. Windows does not expects anything from these bytes (should it be data from the first block, or the last one, or some mix), but uses them somehow. It leads to non-determinism of the guest execution, because block driver does not preserve any order of reading. This situation was discusses in the mailing list at least twice: https://lists.gnu.org/archive/html/qemu-devel/2010-09/msg01996.html https://lists.gnu.org/archive/html/qemu-devel/2020-02/msg05185.html This patch makes such disk reads deterministic in icount mode. It splits the whole request into several parts. Parts may overlap, but SGs inside one part do not overlap. Parts that are processed later overwrite the prior ones in case of overlapping. Examples for different SG part sequences: 1) A1 1000 A2 1000 A1 1000 A3 1000 -> One request is split into two. A1 1000 A2 1000 -- A1 1000 A3 1000 2) A1 800 A2 1000 A1 1000 -> A1 800 A2 1000 -- A1 1000 Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru> Message-Id: <159117972206.12193.12939621311413561779.stgit@pasha-ThinkPad-X280> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'dma-helpers.c')
-rw-r--r--dma-helpers.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/dma-helpers.c b/dma-helpers.c
index e8a26e81e1..2a77b5a9cb 100644
--- a/dma-helpers.c
+++ b/dma-helpers.c
@@ -13,6 +13,8 @@
#include "trace-root.h"
#include "qemu/thread.h"
#include "qemu/main-loop.h"
+#include "sysemu/cpus.h"
+#include "qemu/range.h"
/* #define DEBUG_IOMMU */
@@ -142,6 +144,26 @@ static void dma_blk_cb(void *opaque, int ret)
cur_addr = dbs->sg->sg[dbs->sg_cur_index].base + dbs->sg_cur_byte;
cur_len = dbs->sg->sg[dbs->sg_cur_index].len - dbs->sg_cur_byte;
mem = dma_memory_map(dbs->sg->as, cur_addr, &cur_len, dbs->dir);
+ /*
+ * Make reads deterministic in icount mode. Windows sometimes issues
+ * disk read requests with overlapping SGs. It leads
+ * to non-determinism, because resulting buffer contents may be mixed
+ * from several sectors. This code splits all SGs into several
+ * groups. SGs in every group do not overlap.
+ */
+ if (mem && use_icount && dbs->dir == DMA_DIRECTION_FROM_DEVICE) {
+ int i;
+ for (i = 0 ; i < dbs->iov.niov ; ++i) {
+ if (ranges_overlap((intptr_t)dbs->iov.iov[i].iov_base,
+ dbs->iov.iov[i].iov_len, (intptr_t)mem,
+ cur_len)) {
+ dma_memory_unmap(dbs->sg->as, mem, cur_len,
+ dbs->dir, cur_len);
+ mem = NULL;
+ break;
+ }
+ }
+ }
if (!mem)
break;
qemu_iovec_add(&dbs->iov, mem, cur_len);