[Qemu-devel] [RFC PATCH v1 20/22] fw_cfg: sev: disable dma in real mode

[Brijesh Singh]

In SEV-enabled guest dma should be performed on shared pages. Since
the SeaBIOS executes in non PAE mode and does not have access to C-bit
to create a shared page hence disable the dma operation when reading
from fw_cfg interface.

Signed-off-by: Brijesh Singh <address@hidden>
---
 hw/nvram/fw_cfg.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 6a68e59..aca99e9 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -24,6 +24,7 @@
 #include "qemu/osdep.h"
 #include "hw/hw.h"
 #include "sysemu/sysemu.h"
+#include "sysemu/kvm.h"
 #include "sysemu/dma.h"
 #include "hw/boards.h"
 #include "hw/isa/isa.h"
@@ -1009,6 +1010,11 @@ static void fw_cfg_io_realize(DeviceState *dev, Error 
**errp)
     FWCfgIoState *s = FW_CFG_IO(dev);
     SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
 
+    /* disable dma on fw_cfg when SEV is enabled */
+    if (kvm_sev_enabled()) {
+        qdev_prop_set_bit(dev, "dma_enabled", false);
+    }
+
     /* when using port i/o, the 8-bit data register ALWAYS overlaps
      * with half of the 16-bit control register. Hence, the total size
      * of the i/o region used is FW_CFG_CTL_SIZE */