Re: [PATCH RESEND v2 18/32] hw/i386/pc_sysfw: Simplify using memory_region_init_alias()

[Paolo Bonzini]

On 25/02/20 11:05, Philippe Mathieu-Daudé wrote:
>>
>> pc_isa_bios_init() does a manual copy of a part of the BIOS,
>> from a read-only region. We can simplify by directly aliasing
>> the same part.
>>
>> Before:
>>
>>    (qemu) info mtree
>>    memory-region: system
>>      0000000000000000-ffffffffffffffff (prio 0, i/o): system
>>        0000000000000000-0000000007ffffff (prio 0, ram): alias
>> ram-below-4g @pc.ram 0000000000000000-0000000007ffffff
>>        0000000000000000-ffffffffffffffff (prio -1, i/o): pci
>>          00000000000a0000-00000000000bffff (prio 1, i/o): vga-lowmem
>>          00000000000c0000-00000000000dffff (prio 1, rom): pc.rom
>>          00000000000e0000-00000000000fffff (prio 1, rom): isa-bios
>>        ...
>>        00000000fff00000-00000000ffffffff (prio 0, romd): system.flash0
>>
>> After:
>>
>>    (qemu) info mtree
>>    memory-region: system
>>      0000000000000000-ffffffffffffffff (prio 0, i/o): system
>>        0000000000000000-0000000007ffffff (prio 0, ram): alias
>> ram-below-4g @pc.ram 0000000000000000-0000000007ffffff
>>        0000000000000000-ffffffffffffffff (prio -1, i/o): pci
>>          00000000000a0000-00000000000bffff (prio 1, i/o): vga-lowmem
>>          00000000000c0000-00000000000dffff (prio 1, rom): pc.rom
>>          00000000000e0000-00000000000fffff (prio 1, romd): alias
>> isa-bios @system.flash0 00000000000e0000-00000000000fffff
>>        ...
>>        00000000fff00000-00000000ffffffff (prio 0, romd): system.flash0
> 
> IIUC migrating old -> new is OK, the previous ROM copy is discarded.
> 
> What about new -> old, does it require specific handling? Do we care?

Old->new is broken because the "isa-bios" memory region is not found.

qemu-system-x86_64: Unknown ramblock "isa-bios", cannot accept migration
qemu-system-x86_64: error while loading state for instance 0x0 of device 'ram'
qemu-system-x86_64: load of migration failed: Invalid argument

Paolo