Re: [Qemu-devel] [PATCH 2/5] exec: qemu_ram_alloc_device, qemu_ram_resize

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/11/2014 15:03, Juan Quintela wrote:
> Paolo Bonzini <pbonzini@redhat.com> wrote:
>> On 19/11/2014 14:49, Juan Quintela wrote:
>>>>> Real hardware lets users update firmware and so should virtual hardware.
>>> But you can hibernate your laptop, update the firmware, and reboot?
>>> Where the change can be anyting, like moving from traditional BIOS to
>>> UEFI?
>>
>> Wait wait wait.  I totally cannot follow.  What would be the equivalent
>> in QEMU?
> 
> qemu-2.0 -M pc-2.0
> 
> migrate to disk/s3/s4
> 
> upgrade qemu
> 
> qemu-2.2 -M pc-2.0
> 
> try interesting variation of s3/s4/migration to disk.  Migration to disk
> should work (we migrate BIOS ROM blocks, enphasis on ROM), s3 perhaps
> (machine needs to be saved to disk), s4 ..... depends how it ends being
> done.

Ok, got it.  S3 + migrate to disk should work.

S4 probably would work, but I think it would work on a real system too
as long as you update software and not hardware (e.g. changing the
motherboard would change the MAC address of the on-board NIC, for example).

Consider the similar case on real hardware:

boot
update microcode RPM
s4
turn on

CPU microcode is installed early by the kernel, before looking for a
hibernation image to resume from, so the CPU microcode after resume from
S4 is different from the microcode at the time you suspended to disk.
This probably would work.

Paolo