Re: [Qemu-devel] [PATCH for-1.5] Revert "pc: Kill the "use flash device for BIOS unless KVM" misfeature"

[Markus Armbruster <armbru@redhat.com>]

Sorry for the delay, I was off for a few days.

Anthony Liguori <aliguori@us.ibm.com> writes:

> Paolo Bonzini <pbonzini@redhat.com> writes:
>
>> This reverts commit 9953f8822cc316eec9962f0a2858c3439a80adec.
>> While Markus's analysis is entirely correct, there are 1.6 patches
>> that fix the bug for real and without requiring machine type hacks.
>> Let's think of the children who will have to read this code, and
>> avoid a complicated mess of semantics that differ between <1.5,
>> 1.5, and >1.5.
>>
>> Conflicts:
>> 	hw/i386/pc_piix.c
>> 	hw/i386/pc_q35.c
>> 	include/hw/i386/pc.h
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>
> Acked-by: Anthony Liguori <aliguori@us.ibm.com>
>
> I was hestitant to apply this but felt that the new semantics would be
> more reasonable.   However, since it looks like we're closer to having
> executable flash than I expected we were, I agree that having special
> semantics for 1.6 is undesirable.
>
> I'll give Markus a chance to chime in though.

My commit fixed a relatively minor bug for a price that I consider quite
fair (or else I wouldn't have fixed it).  The increase in ugliness of
the machine type compatiblity machinery is real, but dwarved by the
preexisting ugliness there.

This commit brings back the bug, because you're unwilling to pay the
price now that there's hope flash can be made to work with KVM in 1.6.

I'm not sure I agree, but I acknowledge it's a defensible argument,
given how long the bug has been around.  In short, it's a judgement
call, and Anthony made it.

Belated patch review inline.

> Regards,
>
> Anthony Liguori
>
>
>> ---
>>  hw/block/pc_sysfw.c  | 8 ++++----
>>  hw/i386/pc_piix.c    | 3 ---
>>  hw/i386/pc_q35.c     | 1 -
>>  include/hw/i386/pc.h | 5 -----
>>  4 files changed, 4 insertions(+), 13 deletions(-)
>>
>> diff --git a/hw/block/pc_sysfw.c b/hw/block/pc_sysfw.c
>> index aad8614..4f17668 100644
>> --- a/hw/block/pc_sysfw.c
>> +++ b/hw/block/pc_sysfw.c

I'm afraid you forgot to delete variable
pc_sysfw_flash_vs_rom_bug_compatible.

>> @@ -209,7 +209,7 @@ void pc_system_firmware_init(MemoryRegion *rom_memory)
>>       * TODO This device exists only so that users can switch between
>>       * use of flash and ROM for the BIOS.  The ability to switch was
>>       * created because flash doesn't work with KVM.  Once it does, we
>> -     * should drop this device for new machine types.
>> +     * should drop this device.
>>       */
>>      sysfw_dev = (PcSysFwDevice*) qdev_create(NULL, "pc-sysfw");
>>  

Why did you change the comment?

>> @@ -226,9 +226,9 @@ void pc_system_firmware_init(MemoryRegion *rom_memory)
>>         Use old rom based firmware initialization for KVM. */
>>      /*
>>       * This is a Bad Idea, because it makes enabling/disabling KVM
>> -     * guest-visible.  Do it only in bug-compatibility mode.
>> +     * guest-visible.  Let's fix it for real in QEMU 1.6.
>>       */
>> -    if (pc_sysfw_flash_vs_rom_bug_compatible && kvm_enabled()) {
>> +    if (kvm_enabled()) {
>>          if (pflash_drv != NULL) {
>>              fprintf(stderr, "qemu: pflash cannot be used with kvm enabled\n");
>>              exit(1);
>> @@ -255,7 +255,7 @@ void pc_system_firmware_init(MemoryRegion *rom_memory)
>>  }
>>  
>>  static Property pcsysfw_properties[] = {
>> -    DEFINE_PROP_UINT8("rom_only", PcSysFwDevice, rom_only, 1),
>> +    DEFINE_PROP_UINT8("rom_only", PcSysFwDevice, rom_only, 0),
>>      DEFINE_PROP_END_OF_LIST(),
>>  };
>>  
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