[Qemu-block] [PATCH] ahci: enable pci bus master MemoryRegion before loading ahci engines

[andychiu]

If Windows 10 guests have enabled 'turn off hard disk after idle'
option in power settings, and the guest has a SATA disk plugged in,
the SATA disk will be turned off after a specified idle time.
If the guest is live migrated or saved/loaded with its SATA disk
turned off, the following error will occur:

qemu-system-x86_64: AHCI: Failed to start FIS receive engine: bad FIS receive 
buffer address
qemu-system-x86_64: Failed to load ich9_ahci:ahci
qemu-system-x86_64: error while loading state for instance 0x0 of device 
'0000:00:1a.0/ich9_ahci'
qemu-system-x86_64: load of migration failed: Operation not permitted

Observation from trace logs shows that a while after Windows 10 turns off
a SATA disk (IDE disks don't have the following behavior),
it will disable the PCI_COMMAND_MASTER flag of the pci device containing
the ahci device. When the the disk is turning back on,
the PCI_COMMAND_MASTER flag will be restored first.
But if the guest is migrated or saved/loaded while the disk is off,
the post_load callback of ahci device, ahci_state_post_load(), will fail
at ahci_cond_start_engines() if the MemoryRegion
pci_dev->bus_master_enable_region is not enabled, with pci_dev pointing
to the PCIDevice struct containing the ahci device.

This patch enables pci_dev->bus_master_enable_region before calling
ahci_cond_start_engines() in ahci_state_post_load(), and restore the
MemoryRegion to its original state afterwards.

Signed-off-by: andychiu <address@hidden>
---
 hw/ide/ahci.c | 53 ++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 36 insertions(+), 17 deletions(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index d45393c..83f8c30 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -1649,33 +1649,52 @@ static const VMStateDescription vmstate_ahci_device = {
     },
 };
 
+static int ahci_state_load_engines(AHCIState *s, AHCIDevice *ad)
+{
+    AHCIPortRegs *pr = &ad->port_regs;
+    DeviceState *dev_state = s->container;
+    PCIDevice *pci_dev = (PCIDevice *) object_dynamic_cast(OBJECT(dev_state),
+                                                           TYPE_PCI_DEVICE);
+    bool pci_bus_master_enabled = pci_dev->bus_master_enable_region.enabled;
+
+    if (!(pr->cmd & PORT_CMD_START) && (pr->cmd & PORT_CMD_LIST_ON)) {
+        error_report("AHCI: DMA engine should be off, but status bit "
+                     "indicates it is still running.");
+        return -1;
+    }
+    if (!(pr->cmd & PORT_CMD_FIS_RX) && (pr->cmd & PORT_CMD_FIS_ON)) {
+        error_report("AHCI: FIS RX engine should be off, but status bit "
+                     "indicates it is still running.");
+        return -1;
+    }
+
+    memory_region_set_enabled(&pci_dev->bus_master_enable_region, true);
+
+    /*
+     * After a migrate, the DMA/FIS engines are "off" and
+     * need to be conditionally restarted
+     */
+    pr->cmd &= ~(PORT_CMD_LIST_ON | PORT_CMD_FIS_ON);
+    if (ahci_cond_start_engines(ad) != 0) {
+        return -1;
+    }
+    memory_region_set_enabled(&pci_dev->bus_master_enable_region,
+                              pci_bus_master_enabled);
+
+    return 0;
+}
+
 static int ahci_state_post_load(void *opaque, int version_id)
 {
     int i, j;
     struct AHCIDevice *ad;
     NCQTransferState *ncq_tfs;
-    AHCIPortRegs *pr;
     AHCIState *s = opaque;
 
     for (i = 0; i < s->ports; i++) {
         ad = &s->dev[i];
-        pr = &ad->port_regs;
-
-        if (!(pr->cmd & PORT_CMD_START) && (pr->cmd & PORT_CMD_LIST_ON)) {
-            error_report("AHCI: DMA engine should be off, but status bit "
-                         "indicates it is still running.");
-            return -1;
-        }
-        if (!(pr->cmd & PORT_CMD_FIS_RX) && (pr->cmd & PORT_CMD_FIS_ON)) {
-            error_report("AHCI: FIS RX engine should be off, but status bit "
-                         "indicates it is still running.");
-            return -1;
-        }
 
-        /* After a migrate, the DMA/FIS engines are "off" and
-         * need to be conditionally restarted */
-        pr->cmd &= ~(PORT_CMD_LIST_ON | PORT_CMD_FIS_ON);
-        if (ahci_cond_start_engines(ad) != 0) {
+        if (ahci_state_load_engines(s, ad)) {
             return -1;
         }
 
-- 
2.7.4