Re: [RFC v4 00/24] Add Realm support to QEMU-VMM

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Tue, Nov 10, 2026 at 05:01:14PM +0900, Kohei Enju wrote:

[...]

> > > > > (1) qemu is terminiated on qmp command 'dump-guest-memory'
> > > > > 
> > > > > (qemu) dump-guest-memory -p "/tmp/mem" 0x40000000 0x10000000
> > > > > **
> > > > > ERROR:../system/memory_mapping.c:215:guest_phys_block_add_section: assertion failed: (predecessor->target_end <= target_start)
> > > > > Bail out! ERROR:../system/memory_mapping.c:215:guest_phys_block_add_section: assertion failed: (predecessor->target_end <= target_start)
> > > > > 
> > > > 
> > > > On my side this command causes the Realm to abort, as I expected it to be.
> 
> Hi Mathieu, Gavin.
> 
> I've tested RFC v5, and I reproduced issue (1) on my side as well:
> 
>     (qemu) dump-guest-memory -p "/tmp/mem" 0x40000000 0x10000000
>     Failed to set KVM_REG_ARM_TIMER_CNT
>     ./qemu-ram-realm.sh: line 21: 77580 Aborted                 (core dumped) $QEMU -no-reboot -M confidential-guest-support=rme0,memory-backend=ram0 ...
> 
> This was resolved by adding kvm-no-adjvtime=on.
> 
> > > > Realm memory should not be observable from the host.  There may be a debug mode
> > > > to enable this kind of operation but I will have to look at the documentation
> > > > for details.
> > > > > (2) qemu emulation can't be stopped and resumed
> > > > > 
> > > > > (qemu) stop
> > > > > (qemu) cont
> > > > > Failed to set KVM_REG_ARM_TIMER_CNT
> > > > > 
> > > > 
> > > > That too I was expecting.  Anything that can comprimise a Realm will cause the
> > > > HW to abort.  I'll investigate the "Failed to set KVM_REG_ARM_TIMER_CNT" error
> > > > message though.
> 
> kvm-no-adjvtime=on also resolved issue (2) above.
> 
> Setting KVM_REG_ARM_TIMER_CNT for Realm VMs is not allowed, so we should
> either add this option or consider making it the default for Realm VMs
> in the future. What do you think?

I think that we should do something like we do for *put_registers(),
where we detect whether we are running a Realm VM or not, regardless
of the command line parameter or default that param to on for Realms.

Lorenzo