Message ID | 159117972206.12193.12939621311413561779.stgit@pasha-ThinkPad-X280 (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [v4] icount: make dma reads deterministic | expand |
Am 03.06.2020 um 12:22 hat Pavel Dovgalyuk geschrieben: > From: Pavel Dovgalyuk <pavel.dovgaluk@gmail.com> > > 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> Thanks, applied to the block branch. Kevin
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);