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

[Markus Armbruster <armbru@redhat.com>]

Jason Andryuk <jandryuk@gmail.com> writes:

> 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()?

commit ebc29e1beab02646702c8cb9a1d29b68f72ad503

    pc: Support firmware configuration with -blockdev

    [...]

    Properties need to be created in .instance_init() methods.  For PC
    machines, that's pc_machine_initfn().  To make alias properties work,
    we need to create the onboard flash devices there, too.  [...]

For context, read the entire commit message.  If you have questions
then, don't hesitate to ask them here.