From 1d05047c15ca1d8e29dcb0892e449987739682b4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
Date: Wed, 13 Dec 2017 13:38:40 +0100
Subject: [PATCH 09/41] fw_cfg: unbreak migration compatibility
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RH-Author: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: <20171213133912.26176-10-marcandre.lureau@redhat.com>
Patchwork-id: 78359
O-Subject: [RHEL-7.5 qemu-kvm PATCH v3 09/41] fw_cfg: unbreak migration compatibility
Bugzilla: 1411490
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

From: Laszlo Ersek <lersek@redhat.com>

Upstream-status: RHEL only

fw_cfg DMA shouldn't be enabled by default on x86, or it will break
migration from new (DMA) to old (non-DMA) qemu.

Thus we must maintain DMA disabled by default. Since we don't
introduce a new machine, only if requested explicitely with -global
fw_cfg.dma_enabled=on, or -device vmcoreinfo (see upcoming RHEL-only
patch) should DMA be enabled.

(this is somewhat similar to upstream commit
e6915b5f3a874a467a9a65f7ec1d6ef8d251a51a, except that we can't enable
DMA by default on RHEL qemu)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/nvram/fw_cfg.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 1789487..a7bc98e 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -677,13 +677,16 @@ fw_cfg_init_dma(uint32_t ctl_port, uint32_t data_port,
     SysBusDevice *d;
     FWCfgState *s;
     uint32_t version = FW_CFG_VERSION;
-    bool dma_enabled = dma_port && dma_as;
+    bool dma_requested = dma_port && dma_as;
 
     dev = qdev_create(NULL, "fw_cfg");
     qdev_prop_set_uint32(dev, "ctl_iobase", ctl_port);
     qdev_prop_set_uint32(dev, "data_iobase", data_port);
     qdev_prop_set_uint32(dev, "dma_iobase", dma_port);
-    qdev_prop_set_bit(dev, "dma_enabled", dma_enabled);
+
+    if (!dma_requested) {
+        qdev_prop_set_bit(dev, "dma_enabled", false);
+    }
 
     d = SYS_BUS_DEVICE(dev);
 
@@ -702,7 +705,7 @@ fw_cfg_init_dma(uint32_t ctl_port, uint32_t data_port,
     if (data_addr) {
         sysbus_mmio_map(d, 1, data_addr);
     }
-    if (dma_enabled) {
+    if (s->dma_enabled) {
         /* 64 bits for the address field */
         s->dma = &dma_context_memory;
         s->dma_addr = 0;
-- 
1.8.3.1