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

[Michael S. Tsirkin]

On Wed, Nov 19, 2014 at 03:20:07PM +0100, Juan Quintela wrote:
> Paolo Bonzini <address@hidden> wrote:
> > On 19/11/2014 15:03, Juan Quintela wrote:
> >> Paolo Bonzini <address@hidden> 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.
> 
> I am not an expert of cpu microcode, but I would assume that changes
> there tend to be minimal, no?  And anyways, I wouldn't expect to
> introduce/remove features like NX (i.e. visible by the guest) on a
> microcode update?
> 
> Later, Juan.
> 
> > Paolo

Not added mostly because there's no point: CPU vendors
would much rather sell you a new CPU :)
Features could be removed because of some errata?

-- 
MST