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[Qemu-devel] Hvmloader: Add _STA for PCI hotplug slots

From: Gonglei (Arei)
Subject: [Qemu-devel] Hvmloader: Add _STA for PCI hotplug slots
Date: Fri, 27 Sep 2013 06:29:20 +0000


In Xen platform, after using upstream qemu, the all of pci devices will show 
hotplug in the windows guest. 
In this situation, the windows guest may occur blue screen when VM' user click 
the icon of VGA card for trying unplug VGA card.
However, we don't hope VM's user can do such dangerous operation, and showing 
all pci devices inside the guest OS is unfriendly.

In addition, I find the traditional qemu have not this problem, and KVM also.

On the KVM platform, the seabios will read the RMV bits of pci slot (according 
the 0xae08 I/O port register), 
then modify the SSDT table. 

The key steps as follows:
In Seabios:
#define PCI_RMV_BASE 0xae0c    // 0xae08 I/O port register
static void* build_ssdt(void)
 // build Device object for each slot
 u32 rmvc_pcrm = inl(PCI_RMV_BASE);

In upstream Qemu, read 0xae0c I/O port register function:
static uint64_t pci_read(void *opaque, hwaddr addr, unsigned int size)
        val = s->pci0_hotplug_enable;
s->pci0_hotplug_enable is set by the follow function:

static void piix4_update_hotplug(PIIX4PMState *s)
        s->pci0_hotplug_enable = ~0;
    s->pci0_slot_device_present = 0;

    QTAILQ_FOREACH_SAFE(kid, &bus->children, sibling, next) {
        DeviceState *qdev = kid->child;
        PCIDevice *pdev = PCI_DEVICE(qdev);
        PCIDeviceClass *pc = PCI_DEVICE_GET_CLASS(pdev);
        int slot = PCI_SLOT(pdev->devfn);
                //setting by PCIDeviceClass *k->no_hotplug
        if (pc->no_hotplug) {
            s->pci0_hotplug_enable &= ~(1U << slot);

        s->pci0_slot_device_present |= (1U << slot);

But, on the XEN platform, ACPI DSDT tables is produced by the hvmloader, 
more details in this patch´╝Ü

# Node ID 1a912ce93b506a185b54fd97986214e6eff8a0bc 
# Parent  6bc03e22f921aadfa7e5cebe92100cb01377947d 
hvmloader/acpi/dsdt: Fix PCI hotplug with the new qemu-xen. 

The ACPI PIIX4 device in QEMU upstream as not the same behavior to 
handle PCI hotplug. This patch introduce the necessary change to the 
DSDT ACPI table to behave as expceted by the new QEMU. 

To switch to this new DSDT table version, there is a new option 
--dm-version to mk_dsdt. 

Change are inspired by SeaBIOS DSDT source code. 

There is few things missing with the new QEMU: 
  - QEMU provide the plugged/unplugged status only per slot (and not 
    per func like qemu-xen-traditionnal. 
  - I did not include the _STA ACPI method that give the status of a 
    device (present, functionning properly) because qemu-xen does not 
    handle it. 
  - I did not include the _RMV method that say if the device can be 
    because the IO port of QEMU that give this status always return 
    true. In 
    SeaBIOS table, they have a specific _RMV method for VGA, ISA that 
    false. But I'm not sure that we can do the same in Xen.

now, I add the _STA method, return the different value according the 0xae08 I/O 
port register on read,
a pci device allow hotplug return 0x1f, a pci device don't allow return 0x1e.
Then the pci devices which don't allow hotplug will not show inside the guest 

Index: tools/firmware/hvmloader/acpi/mk_dsdt.c
--- tools/firmware/hvmloader/acpi/mk_dsdt.c     (revision 1105)
+++ tools/firmware/hvmloader/acpi/mk_dsdt.c     (working copy)
@@ -437,6 +437,10 @@
         indent(); printf("B0EJ, 32,\n");
+        stmt("OperationRegion", "SRMV, SystemIO, 0xae0c, 0x04");
+        push_block("Field", "SRMV, DWordAcc, NoLock, WriteAsZeros");
+        indent(); printf("RMV, 32,\n");
+        pop_block();        
         /* hotplug_slot */
         for (slot = 1; slot <= 31; slot++) {
             push_block("Device", "S%i", slot); {
@@ -445,6 +449,14 @@
                     stmt("Store", "ShiftLeft(1, %#06x), B0EJ", slot);
                     stmt("Return", "0x0");
                 } pop_block();
+                push_block("Method", "_STA, 0");{
+                   push_block("If", "And(RMV, ShiftLeft(1, %#06x))", slot);
+                      stmt("Return", "0x1F");
+                   pop_block();
+                   push_block("Else", NULL);
+                      stmt("Return", "0x1E");
+                   pop_block();
+                };pop_block();
                 stmt("Name", "_SUN, %i", slot);
             } pop_block();

Have you any ideas´╝čExpecting your reply, thanks in advance!

Best regards,

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