Re: [PATCH v1 01/14] s390x/s390-virtio-ccw: don't crash on weird RAM sizes

[David Hildenbrand]

On 11.09.24 14:46, Thomas Huth wrote:
> On 11/09/2024 14.38, David Hildenbrand wrote:
> > On 11.09.24 13:28, Janosch Frank wrote:
> > > On 9/10/24 7:57 PM, David Hildenbrand wrote:
> > > > KVM is not happy when starting a VM with weird RAM sizes:
> > > >
> > > >      # qemu-system-s390x --enable-kvm --nographic -m 1234K
> > > >      qemu-system-s390x: kvm_set_user_memory_region:
> > > > KVM_SET_USER_MEMORY_REGION
> > > >        failed, slot=0, start=0x0, size=0x244000: Invalid argument
> > > >      kvm_set_phys_mem: error registering slot: Invalid argument
> > > >      Aborted (core dumped)
> > > >
> > > > Let's handle that in a better way by rejecting such weird RAM sizes
> > > > right from the start:
> > >
> > > Huh, I always assumed that ram is handled in multiples of 1MB in QEMU.
> >
> > Me as well, I did not dig if that changed at some point ... or why such odd
> > sizes would even be required :)
>
> I guess it's there for some old PC hardware ... Remember, 640K ought to be
> enough for anybody.

True, maybe the "default to MiB" made some of us believe that something
smaller is impossible :)

And in fact, I think suffix support was added in

commit 6e1d3c1c855818a6d1399698572afae0d11b872b
Author: Igor Mammedov <imammedo@redhat.com>
Date:   Wed Nov 27 01:27:35 2013 +0100

    vl: convert -m to QemuOpts
    
    Adds option to -m
     "size" - startup memory amount
    
    For compatibility with legacy CLI if suffix-less number is passed,
    it assumes amount in Mb.
    
    Otherwise user is free to use suffixed number using suffixes b,k/K,M,G


--
Cheers,

David / dhildenb