Re: [Qemu-devel] [PATCH V2 2/4] pci: reserve 64 bit MMIO range for PCI hotplug

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 18, 2016 at 06:01:15PM +0300, Marcel Apfelbaum wrote:
> On 05/18/2016 05:57 PM, Michael S. Tsirkin wrote:
> >On Wed, May 18, 2016 at 05:43:37PM +0300, Marcel Apfelbaum wrote:
> >>On 05/18/2016 05:14 PM, Michael S. Tsirkin wrote:
> >>>On Sun, May 15, 2016 at 10:23:32PM +0300, Marcel Apfelbaum wrote:
> >>>>Using the firmware assigned MMIO ranges for 64-bit PCI window
> >>>>leads to zero space for hot-plugging PCI devices over 4G.
> >>>>
> >>>>PC machines can use the whole CPU addressable range after
> >>>>the space reserved for memory-hotplug.
> >>>>
> >>>>Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
> >>>>---
> >>>>  hw/pci/pci.c | 16 ++++++++++++++--
> >>>>  1 file changed, 14 insertions(+), 2 deletions(-)
> >>>>
> >>>>diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> >>>>index bb605ef..44dd949 100644
> >>>>--- a/hw/pci/pci.c
> >>>>+++ b/hw/pci/pci.c
> >>>>@@ -41,6 +41,7 @@
> >>>>  #include "hw/hotplug.h"
> >>>>  #include "hw/boards.h"
> >>>>  #include "qemu/cutils.h"
> >>>>+#include "hw/i386/pc.h"
> >>>>
> >>>>  //#define DEBUG_PCI
> >>>>  #ifdef DEBUG_PCI
> >>>
> >>>I don't want pci to depend on PC.
> >>>Pls find another way to do this.
> >>>
> >>
> >>Igor has an idea to not call pci_dev_get_w64 and make the computations
> >>in the acpi code. I'll follow this idea.
> >>
> >>>
> >>>>@@ -2467,8 +2468,19 @@ static void pci_dev_get_w64(PCIBus *b, PCIDevice *dev, void *opaque)
> >>>>
> >>>>  void pci_bus_get_w64_range(PCIBus *bus, Range *range)
> >>>>  {
> >>>>-    range->begin = range->end = 0;
> >>>>-    pci_for_each_device_under_bus(bus, pci_dev_get_w64, range);
> >>>>+    Object *machine = qdev_get_machine();
> >>>An empty line won't hurt here after the declaration.
> >>>
> >>>>+    if (object_dynamic_cast(machine, TYPE_PC_MACHINE)) {
> >>>>+        PCMachineState *pcms = PC_MACHINE(machine);
> >>>
> >>>An empty line won't hurt here after the declaration.
> >>>
> >>>>+        range->begin = pc_machine_get_reserved_memory_end(pcms);
> >>>>+        if (!range->begin) {
> >>>>+            range->begin = ROUND_UP(0x100000000ULL + pcms->above_4g_mem_size,
> >>>>+                                    1ULL << 30);
> >>>
> >>>Why 30? what is the logic here?
> >>>
> >>
> >>Will put it inside pci_dev_get_w64 and explain.
> >>
> >>>>+        }
> >>>>+        range->end = 1ULL << 40; /* 40 bits physical */
> >>>
> >>>This comment does not help. Physical what? And why is 40 bit right?
> >>
> >>It refers to how many bits are CPU addressable. (I will add a better comment)
> >>cpu_x86_cpuid from target-i386/cpu.c it always returns 40
> >>so hard-coding it looked like a safe choice.
> >>
> >>Thanks,
> >>Marcel
> >
> >Besides being ugly (we should get this from CPU code, not hard-code it)
> >not all guests look at CPUID unfortunately.
> >E.g. try win7 32 bit.
> >
> 
> I am open to better ideas, can you please advice?
> 
> Thanks,
> Marcel

I'm afraid you will have to try a ton of guests and collect 
data on which window ranges make them crash :(

> >
> >>>>+    } else {
> >>>>+        range->begin = range->end = 0;
> >>>>+        pci_for_each_device_under_bus(bus, pci_dev_get_w64, range);
> >>>
> >>>When does this trigger?
> >>>Pls add a comment.
> >>>
> >>>>+    }
> >>>>  }
> >>>>
> >>>>  static bool pcie_has_upstream_port(PCIDevice *dev)
> >>>>--
> >>>>2.4.3