[RFC PATCH v2 2/2] memory: set engaged_in_io when a device calls DMA APIs

[Alexander Bulekov]

DMA reentrancy problems can occur in BHs:
dev_mmio->schedule_bh
dev_bh->dma_write->dev_mmio

This patch attempts to address this scenario by marking the device as
engaged_in_io, when it calls into PCI and SGList DMA APIs.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 include/hw/pci/pci.h  | 6 +++++-
 softmmu/dma-helpers.c | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index e7cdf2d5ec..8420984b23 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -808,7 +808,11 @@ static inline MemTxResult pci_dma_rw(PCIDevice *dev, 
dma_addr_t addr,
                                      void *buf, dma_addr_t len,
                                      DMADirection dir)
 {
-    return dma_memory_rw(pci_get_address_space(dev), addr, buf, len, dir);
+    MemTxResult result;
+    dev->qdev.engaged_in_io = true;
+    result = dma_memory_rw(pci_get_address_space(dev), addr, buf, len, dir);
+    dev->qdev.engaged_in_io = false;
+    return result;
 }
 
 /**
diff --git a/softmmu/dma-helpers.c b/softmmu/dma-helpers.c
index 7d766a5e89..dd27ba4def 100644
--- a/softmmu/dma-helpers.c
+++ b/softmmu/dma-helpers.c
@@ -303,6 +303,7 @@ static uint64_t dma_buf_rw(uint8_t *ptr, int32_t len, 
QEMUSGList *sg,
     resid = sg->size;
     sg_cur_index = 0;
     len = MIN(len, resid);
+    sg->dev->engaged_in_io = true;
     while (len > 0) {
         ScatterGatherEntry entry = sg->sg[sg_cur_index++];
         int32_t xfer = MIN(len, entry.len);
@@ -311,6 +312,7 @@ static uint64_t dma_buf_rw(uint8_t *ptr, int32_t len, 
QEMUSGList *sg,
         len -= xfer;
         resid -= xfer;
     }
+    sg->dev->engaged_in_io = true;
 
     return resid;
 }
-- 
2.33.0