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

[Jason Andryuk <jandryuk@gmail.com>]

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?
"""

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 */
> > >>>
> > >
> > >
>
>