Re: [PATCH 15/15] hw/i386/pc_piix: Move i440fx' realize near its qdev_new()

[Bernhard Beschow]

Am 13. Juni 2023 09:52:50 UTC schrieb Igor Mammedov <imammedo@redhat.com>:
>On Mon, 12 Jun 2023 17:49:10 +0000
>Bernhard Beschow <shentey@gmail.com> wrote:
>
>> Am 12. Juni 2023 15:21:19 UTC schrieb Igor Mammedov <imammedo@redhat.com>:
>> >On Mon, 12 Jun 2023 16:51:55 +0200
>> >Igor Mammedov <imammedo@redhat.com> wrote:
>> >  
>> >> On Sun, 11 Jun 2023 12:34:12 +0200
>> >> Bernhard Beschow <shentey@gmail.com> wrote:
>> >>   
>> >> > I440FX realization is currently mixed with PIIX3 creation. Furthermore, 
>> >> > it is
>> >> > common practice to only set properties between a device's qdev_new() and
>> >> > qdev_realize(). Clean up to resolve both issues.
>> >> > 
>> >> > Since I440FX spawns a PCI bus let's also move the pci_bus 
>> >> > initialization there.
>> >> > 
>> >> > Note that when running `qemu-system-x86_64 -M pc -S` before and after 
>> >> > this
>> >> > patch, `info mtree` in the QEMU console doesn't show any differences 
>> >> > except that
>> >> > the ordering is different.
>> >> > 
>> >> > Signed-off-by: Bernhard Beschow <shentey@gmail.com>
>> >> > ---
>> >> >  hw/i386/pc_piix.c | 57 ++++++++++++++++++++++++-----------------------
>> >> >  1 file changed, 29 insertions(+), 28 deletions(-)
>> >> > 
>> >> > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
>> >> > index 22173b122b..23b9725c94 100644
>> >> > --- a/hw/i386/pc_piix.c
>> >> > +++ b/hw/i386/pc_piix.c
>> >> > @@ -126,7 +126,6 @@ static void pc_init1(MachineState *machine,
>> >> >      MemoryRegion *rom_memory;
>> >> >      ram_addr_t lowmem;
>> >> >      uint64_t hole64_size;
>> >> > -    Object *i440fx_host;
>> >> >  
>> >> >      /*
>> >> >       * Calculate ram split, for memory below and above 4G.  It's a bit
>> >> > @@ -198,17 +197,43 @@ static void pc_init1(MachineState *machine,
>> >> >      }
>> >> >  
>> >> >      if (pcmc->pci_enabled) {
>> >> > +        Object *phb;
>> >> > +
>> >> >          pci_memory = g_new(MemoryRegion, 1);
>> >> >          memory_region_init(pci_memory, NULL, "pci", UINT64_MAX);
>> >> >          rom_memory = pci_memory;
>> >> > -        i440fx_host = OBJECT(qdev_new(host_type));
>> >> > -        hole64_size = object_property_get_uint(i440fx_host,
>> >> > +
>> >> > +        phb = OBJECT(qdev_new(host_type));
>> >> > +        object_property_add_child(OBJECT(machine), "i440fx", phb);
>> >> > +        object_property_set_link(phb, PCI_HOST_PROP_RAM_MEM,
>> >> > +                                 OBJECT(ram_memory), &error_fatal);
>> >> > +        object_property_set_link(phb, PCI_HOST_PROP_PCI_MEM,
>> >> > +                                 OBJECT(pci_memory), &error_fatal);
>> >> > +        object_property_set_link(phb, PCI_HOST_PROP_SYSTEM_MEM,
>> >> > +                                 OBJECT(system_memory), &error_fatal);
>> >> > +        object_property_set_link(phb, PCI_HOST_PROP_IO_MEM,
>> >> > +                                 OBJECT(system_io), &error_fatal);
>> >> > +        object_property_set_uint(phb, PCI_HOST_BELOW_4G_MEM_SIZE,
>> >> > +                                 x86ms->below_4g_mem_size, 
>> >> > &error_fatal);
>> >> > +        object_property_set_uint(phb, PCI_HOST_ABOVE_4G_MEM_SIZE,
>> >> > +                                 x86ms->above_4g_mem_size, 
>> >> > &error_fatal);
>> >> > +        object_property_set_str(phb, I440FX_HOST_PROP_PCI_TYPE, 
>> >> > pci_type,
>> >> > +                                &error_fatal);
>> >> > +        sysbus_realize_and_unref(SYS_BUS_DEVICE(phb), &error_fatal);
>> >> > +
>> >> > +        pci_bus = PCI_BUS(qdev_get_child_bus(DEVICE(phb), "pci.0"));
>> >> > +        pci_bus_map_irqs(pci_bus,
>> >> > +                         xen_enabled() ? xen_pci_slot_get_pirq
>> >> > +                                       : pc_pci_slot_get_pirq);
>> >> > +        pcms->bus = pci_bus;
>> >> > +
>> >> > +        hole64_size = object_property_get_uint(phb,
>> >> >                                                 
>> >> > PCI_HOST_PROP_PCI_HOLE64_SIZE,
>> >> >                                                 &error_abort);    
>> >> 
>> >> before patch memory region links were set after the original
>> >> regions were initialized by pc_memory_init(), but after this
>> >> patch you 1st set links and only later pc_memory_init().
>> >> I doesn't look to me as a safe thing to do.  
>> >
>> >or maybe it doesn't matter, but still I have hard time
>> >convincing myself that it is so.   
>> 
>> AFAICS both pc_memory_init() and i440fx_pcihost_realize() rely on 
>> memory_region_init*() having been called on these pointers already. All they 
>> seem to do is adding their sub regions. The order in which this happens 
>> seems to be irrelevant, otherwise we'd see changes in the QOM console calls 
>> I guess.
>
>that's why I said it might not matter, but  ...
>the thing is that now mapping into AS happens in reversed order
>and with overlapped mappings reversed I'm quite unsure if
>that is correct.

Hi Igor,

sorry for the late answer. I think I have missed your reply so far due to KVM 
forum ;)

The order in which the overlapped mappings are added shouldn't matter as long 
as different priorities are supplied. AFAIR adding overlapping regions with the 
same priority would be a programming mistake (in existing code). To rule this 
out I compared the memory mappings before and after the patch and put the 
result in the commit message. It was the same for `info mtree -f`: no 
difference except the order of the printout.

I might be able to send an updated version of this series later today. If you'd 
have further comments after it is out we can continue discussing there.

Best regards,
Bernhard

>
>> 
>> >  
>> >>   
>> >> >      } else {    
>> >> 
>> >>   
>> >> >          pci_memory = NULL;
>> >> >          rom_memory = system_memory;
>> >> > -        i440fx_host = NULL;
>> >> > +        pci_bus = NULL;
>> >> >          hole64_size = 0;    
>> >> 
>> >> is it possible to turn these into initializers, and get rid of 
>> >> 'else'  branch?  
>> 
>> Sure, this is possible. I'd add another patch before this one.
>> 
>> Best regards,
>> Bernhard
>> >>   
>> >> >      }
>> >> >  
>> >> > @@ -243,29 +268,6 @@ static void pc_init1(MachineState *machine,
>> >> >          PIIX3State *piix3;
>> >> >          PCIDevice *pci_dev;
>> >> >  
>> >> > -        object_property_add_child(OBJECT(machine), "i440fx", 
>> >> > i440fx_host);
>> >> > -        object_property_set_link(i440fx_host, PCI_HOST_PROP_RAM_MEM,
>> >> > -                                 OBJECT(ram_memory), &error_fatal);
>> >> > -        object_property_set_link(i440fx_host, PCI_HOST_PROP_PCI_MEM,
>> >> > -                                 OBJECT(pci_memory), &error_fatal);
>> >> > -        object_property_set_link(i440fx_host, PCI_HOST_PROP_SYSTEM_MEM,
>> >> > -                                 OBJECT(system_memory), &error_fatal);
>> >> > -        object_property_set_link(i440fx_host, PCI_HOST_PROP_IO_MEM,
>> >> > -                                 OBJECT(system_io), &error_fatal);
>> >> > -        object_property_set_uint(i440fx_host, 
>> >> > PCI_HOST_BELOW_4G_MEM_SIZE,
>> >> > -                                 x86ms->below_4g_mem_size, 
>> >> > &error_fatal);
>> >> > -        object_property_set_uint(i440fx_host, 
>> >> > PCI_HOST_ABOVE_4G_MEM_SIZE,
>> >> > -                                 x86ms->above_4g_mem_size, 
>> >> > &error_fatal);
>> >> > -        object_property_set_str(i440fx_host, I440FX_HOST_PROP_PCI_TYPE,
>> >> > -                                pci_type, &error_fatal);
>> >> > -        sysbus_realize_and_unref(SYS_BUS_DEVICE(i440fx_host), 
>> >> > &error_fatal);
>> >> > -
>> >> > -        pci_bus = PCI_BUS(qdev_get_child_bus(DEVICE(i440fx_host), 
>> >> > "pci.0"));
>> >> > -        pci_bus_map_irqs(pci_bus,
>> >> > -                         xen_enabled() ? xen_pci_slot_get_pirq
>> >> > -                                       : pc_pci_slot_get_pirq);
>> >> > -        pcms->bus = pci_bus;
>> >> > -
>> >> >          pci_dev = pci_create_simple_multifunction(pci_bus, -1, true,
>> >> >                                                    TYPE_PIIX3_DEVICE);
>> >> >  
>> >> > @@ -290,7 +292,6 @@ static void pc_init1(MachineState *machine,
>> >> >          rtc_state = 
>> >> > ISA_DEVICE(object_resolve_path_component(OBJECT(pci_dev),
>> >> >                                                               "rtc"));
>> >> >      } else {
>> >> > -        pci_bus = NULL;
>> >> >          isa_bus = isa_bus_new(NULL, system_memory, system_io,
>> >> >                                &error_abort);
>> >> >      
>> >>   
>> >  
>> 
>