Re: [PATCH 2/2] xen: cleanup unrealized flash devices

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 7/1/20 2:40 PM, Philippe Mathieu-Daudé wrote:
> On 7/1/20 2:25 PM, Jason Andryuk wrote:
>> On Wed, Jul 1, 2020 at 3:03 AM Paul Durrant <xadimgnik@gmail.com> wrote:
>>>
>>>> -----Original Message-----
>>>> From: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>> Sent: 30 June 2020 18:27
>>>> To: paul@xen.org; xen-devel@lists.xenproject.org; qemu-devel@nongnu.org
>>>> Cc: 'Eduardo Habkost' <ehabkost@redhat.com>; 'Michael S. Tsirkin' <mst@redhat.com>; 'Paul Durrant'
>>>> <pdurrant@amazon.com>; 'Jason Andryuk' <jandryuk@gmail.com>; 'Paolo Bonzini' <pbonzini@redhat.com>;
>>>> 'Richard Henderson' <rth@twiddle.net>
>>>> Subject: Re: [PATCH 2/2] xen: cleanup unrealized flash devices
>>>>
>>>> On 6/30/20 5:44 PM, Paul Durrant wrote:
>>>>>> -----Original Message-----
>>>>>> From: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>>> Sent: 30 June 2020 16:26
>>>>>> To: Paul Durrant <paul@xen.org>; xen-devel@lists.xenproject.org; qemu-devel@nongnu.org
>>>>>> Cc: Eduardo Habkost <ehabkost@redhat.com>; Michael S. Tsirkin <mst@redhat.com>; Paul Durrant
>>>>>> <pdurrant@amazon.com>; Jason Andryuk <jandryuk@gmail.com>; Paolo Bonzini <pbonzini@redhat.com>;
>>>>>> Richard Henderson <rth@twiddle.net>
>>>>>> Subject: Re: [PATCH 2/2] xen: cleanup unrealized flash devices
>>>>>>
>>>>>> On 6/24/20 2:18 PM, Paul Durrant wrote:
>>>>>>> From: Paul Durrant <pdurrant@amazon.com>
>>>>>>>
>>>>>>> The generic pc_machine_initfn() calls pc_system_flash_create() which creates
>>>>>>> 'system.flash0' and 'system.flash1' devices. These devices are then realized
>>>>>>> by pc_system_flash_map() which is called from pc_system_firmware_init() which
>>>>>>> itself is called via pc_memory_init(). The latter however is not called when
>>>>>>> xen_enable() is true and hence the following assertion fails:
>>>>>>>
>>>>>>> qemu-system-i386: hw/core/qdev.c:439: qdev_assert_realized_properly:
>>>>>>> Assertion `dev->realized' failed
>>>>>>>
>>>>>>> These flash devices are unneeded when using Xen so this patch avoids the
>>>>>>> assertion by simply removing them using pc_system_flash_cleanup_unused().
>>>>>>>
>>>>>>> Reported-by: Jason Andryuk <jandryuk@gmail.com>
>>>>>>> Fixes: ebc29e1beab0 ("pc: Support firmware configuration with -blockdev")
>>>>>>> Signed-off-by: Paul Durrant <pdurrant@amazon.com>
>>>>>>> Tested-by: Jason Andryuk <jandryuk@gmail.com>
>>>>>>> ---
>>>>>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>>>>>> Cc: Richard Henderson <rth@twiddle.net>
>>>>>>> Cc: Eduardo Habkost <ehabkost@redhat.com>
>>>>>>> Cc: "Michael S. Tsirkin" <mst@redhat.com>
>>>>>>> Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
>>>>>>> ---
>>>>>>>  hw/i386/pc_piix.c    | 9 ++++++---
>>>>>>>  hw/i386/pc_sysfw.c   | 2 +-
>>>>>>>  include/hw/i386/pc.h | 1 +
>>>>>>>  3 files changed, 8 insertions(+), 4 deletions(-)
>>>>>>>
>>>>>>> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
>>>>>>> index 1497d0e4ae..977d40afb8 100644
>>>>>>> --- a/hw/i386/pc_piix.c
>>>>>>> +++ b/hw/i386/pc_piix.c
>>>>>>> @@ -186,9 +186,12 @@ static void pc_init1(MachineState *machine,
>>>>>>>      if (!xen_enabled()) {
>>>>>>>          pc_memory_init(pcms, system_memory,
>>>>>>>                         rom_memory, &ram_memory);
>>>>>>> -    } else if (machine->kernel_filename != NULL) {
>>>>>>> -        /* For xen HVM direct kernel boot, load linux here */
>>>>>>> -        xen_load_linux(pcms);
>>>>>>> +    } else {
>>>>>>> +        pc_system_flash_cleanup_unused(pcms);
>>>>>>
>>>>>> TIL pc_system_flash_cleanup_unused().
>>>>>>
>>>>>> What about restricting at the source?
>>>>>>
>>>>>
>>>>> And leave the devices in place? They are not relevant for Xen, so why not clean up?
>>>>
>>>> No, I meant to not create them in the first place, instead of
>>>> create+destroy.
>>>>
>>>> Anyway what you did works, so I don't have any problem.
>>>
>>> IIUC Jason originally tried restricting creation but encountered a problem because xen_enabled() would always return false at that point, because machine creation occurs before accelerators are initialized.
>>
>> Correct.  Quoting my previous email:
>> """
>> Removing the call to pc_system_flash_create() from pc_machine_initfn()
>> lets QEMU startup and run a Xen HVM again.  xen_enabled() doesn't work
>> there since accelerators have not been initialized yes, I guess?
> 
> Ah, I missed that. You pointed at the bug here :)
> 
> I think pc_system_flash_create() shouldn't be called in init() but
> realize().

Hmm this is a MachineClass, not qdev, so no realize().

In softmmu/vl.c we have:

4152     configure_accelerators(argv[0]);
....
4327     if (!xen_enabled()) { // so xen_enable() is working
4328         /* On 32-bit hosts, QEMU is limited by virtual address space */
4329         if (ram_size > (2047 << 20) && HOST_LONG_BITS == 32) {
4330             error_report("at most 2047 MB RAM can be simulated");
4331             exit(1);
4332         }
4333     }
....
4348     machine_run_board_init(current_machine);

which calls in hw/core/machine.c:

1089 void machine_run_board_init(MachineState *machine)
1090 {
1091     MachineClass *machine_class = MACHINE_GET_CLASS(machine);
....
1138     machine_class->init(machine);
1139 }

         -> pc_machine_class_init()

This should come after:

         -> pc_machine_initfn()

            -> pc_system_flash_create(pcms)
> 
>> """
>>
>> If you want to remove the creation in the first place, then I have two
>> questions.  Why does pc_system_flash_create()/pc_pflash_create() get
>> called so early creating the pflash devices?  Why aren't they just
>> created as needed in pc_system_flash_map()?
>>
>> Regards,
>> Jason
>>
>>>   Paul
>>>
>>>>
>>>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>
>>>>>
>>>>>   Paul
>>>>>
>>>>>> -- >8 --
>>>>>> --- a/hw/i386/pc.c
>>>>>> +++ b/hw/i386/pc.c
>>>>>> @@ -1004,24 +1004,26 @@ void pc_memory_init(PCMachineState *pcms,
>>>>>>                                      &machine->device_memory->mr);
>>>>>>      }
>>>>>>
>>>>>> -    /* Initialize PC system firmware */
>>>>>> -    pc_system_firmware_init(pcms, rom_memory);
>>>>>> -
>>>>>> -    option_rom_mr = g_malloc(sizeof(*option_rom_mr));
>>>>>> -    memory_region_init_ram(option_rom_mr, NULL, "pc.rom", PC_ROM_SIZE,
>>>>>> -                           &error_fatal);
>>>>>> -    if (pcmc->pci_enabled) {
>>>>>> -        memory_region_set_readonly(option_rom_mr, true);
>>>>>> -    }
>>>>>> -    memory_region_add_subregion_overlap(rom_memory,
>>>>>> -                                        PC_ROM_MIN_VGA,
>>>>>> -                                        option_rom_mr,
>>>>>> -                                        1);
>>>>>> -
>>>>>>      fw_cfg = fw_cfg_arch_create(machine,
>>>>>>                                  x86ms->boot_cpus, x86ms->apic_id_limit);
>>>>>>
>>>>>> -    rom_set_fw(fw_cfg);
>>>>>> +    /* Initialize PC system firmware */
>>>>>> +    if (!xen_enabled()) {
>>>>>> +        pc_system_firmware_init(pcms, rom_memory);
>>>>>> +
>>>>>> +        option_rom_mr = g_malloc(sizeof(*option_rom_mr));
>>>>>> +        memory_region_init_ram(option_rom_mr, NULL, "pc.rom", PC_ROM_SIZE,
>>>>>> +                               &error_fatal);
>>>>>> +        if (pcmc->pci_enabled) {
>>>>>> +            memory_region_set_readonly(option_rom_mr, true);
>>>>>> +        }
>>>>>> +        memory_region_add_subregion_overlap(rom_memory,
>>>>>> +                                            PC_ROM_MIN_VGA,
>>>>>> +                                            option_rom_mr,
>>>>>> +                                            1);
>>>>>> +
>>>>>> +        rom_set_fw(fw_cfg);
>>>>>> +    }
>>>>>>
>>>>>>      if (pcmc->has_reserved_memory && machine->device_memory->base) {
>>>>>>          uint64_t *val = g_malloc(sizeof(*val));
>>>>>> ---
>>>>>>
>>>>>>> +        if (machine->kernel_filename != NULL) {
>>>>>>> +            /* For xen HVM direct kernel boot, load linux here */
>>>>>>> +            xen_load_linux(pcms);
>>>>>>> +        }
>>>>>>>      }
>>>>>>>
>>>>>>>      gsi_state = pc_gsi_create(&x86ms->gsi, pcmc->pci_enabled);
>>>>>>> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
>>>>>>> index ec2a3b3e7e..0ff47a4b59 100644
>>>>>>> --- a/hw/i386/pc_sysfw.c
>>>>>>> +++ b/hw/i386/pc_sysfw.c
>>>>>>> @@ -108,7 +108,7 @@ void pc_system_flash_create(PCMachineState *pcms)
>>>>>>>      }
>>>>>>>  }
>>>>>>>
>>>>>>> -static void pc_system_flash_cleanup_unused(PCMachineState *pcms)
>>>>>>> +void pc_system_flash_cleanup_unused(PCMachineState *pcms)
>>>>>>>  {
>>>>>>>      char *prop_name;
>>>>>>>      int i;
>>>>>>> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
>>>>>>> index e6135c34d6..497f2b7ab7 100644
>>>>>>> --- a/include/hw/i386/pc.h
>>>>>>> +++ b/include/hw/i386/pc.h
>>>>>>> @@ -187,6 +187,7 @@ int cmos_get_fd_drive_type(FloppyDriveType fd0);
>>>>>>>
>>>>>>>  /* pc_sysfw.c */
>>>>>>>  void pc_system_flash_create(PCMachineState *pcms);
>>>>>>> +void pc_system_flash_cleanup_unused(PCMachineState *pcms);
>>>>>>>  void pc_system_firmware_init(PCMachineState *pcms, MemoryRegion *rom_memory);
>>>>>>>
>>>>>>>  /* acpi-build.c */
>>>>>>>
>>>>>
>>>>>
>>>
>>>
>>
>