82fab5c5b9
From an architecture point of view, nothing can be mapped into the address
space on s390x. All there is is memory. Therefore there is also not really
an interface to communicate such information to the guest. All we can do is
specify the maximum ram address and guests can probe in that range if
memory is available and usable (TPROT).
Also memory hotplug is strange. The guest can decide at some point in
time to add / remove memory in some range. While the hypervisor can deny
to online an increment, all increments have to be predefined and there is
no way of telling the guest about a newly "hotplugged" increment. So if we
specify right now e.g.
-m 2G,slots=2,maxmem=20G
An ordinary fedora guest will happily online (hotplug) all memory,
resulting in a guest consuming 20G. So it really behaves rather like
-m 22G
There is no way to hotplug memory from the outside like on other
architectures. This is of course bad for upper management layers.
As the guest can create/delete memory regions while it is running, of
course migration support is not available and tricky to implement.
With virtualization, it is different. We might want to map something
into guest address space (e.g. fake DAX devices) and not detect it
automatically as memory. So we really want to use the maxmem and slots
parameter just like on all other architectures. Such devices will have
to expose the applicable memory range themselves. To finally be able to
provide memory hotplug to guests, we will need a new paravirtualized
interface to do that (e.g. something into the direction of virtio-mem).
This implies, that maxmem cannot be used for s390x memory hotplug
anymore and has to go. This simplifies the code quite a bit.
As migration support is not working, this change cannot really break
migration as guests without slots and maxmem don't see the SCLP
features. Also, the ram size calculation does not change.
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180219174231.10874-1-david@redhat.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
[CH: tweaked patch description, as discussed on list]
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
QEMU README
===========
QEMU is a generic and open source machine & userspace emulator and
virtualizer.
QEMU is capable of emulating a complete machine in software without any
need for hardware virtualization support. By using dynamic translation,
it achieves very good performance. QEMU can also integrate with the Xen
and KVM hypervisors to provide emulated hardware while allowing the
hypervisor to manage the CPU. With hypervisor support, QEMU can achieve
near native performance for CPUs. When QEMU emulates CPUs directly it is
capable of running operating systems made for one machine (e.g. an ARMv7
board) on a different machine (e.g. an x86_64 PC board).
QEMU is also capable of providing userspace API virtualization for Linux
and BSD kernel interfaces. This allows binaries compiled against one
architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a
different architecture ABI (e.g. the Linux x86_64 ABI). This does not
involve any hardware emulation, simply CPU and syscall emulation.
QEMU aims to fit into a variety of use cases. It can be invoked directly
by users wishing to have full control over its behaviour and settings.
It also aims to facilitate integration into higher level management
layers, by providing a stable command line interface and monitor API.
It is commonly invoked indirectly via the libvirt library when using
open source applications such as oVirt, OpenStack and virt-manager.
QEMU as a whole is released under the GNU General Public License,
version 2. For full licensing details, consult the LICENSE file.
Building
========
QEMU is multi-platform software intended to be buildable on all modern
Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety
of other UNIX targets. The simple steps to build QEMU are:
mkdir build
cd build
../configure
make
Additional information can also be found online via the QEMU website:
https://qemu.org/Hosts/Linux
https://qemu.org/Hosts/Mac
https://qemu.org/Hosts/W32
Submitting patches
==================
The QEMU source code is maintained under the GIT version control system.
git clone git://git.qemu.org/qemu.git
When submitting patches, the preferred approach is to use 'git
format-patch' and/or 'git send-email' to format & send the mail to the
qemu-devel@nongnu.org mailing list. All patches submitted must contain
a 'Signed-off-by' line from the author. Patches should follow the
guidelines set out in the HACKING and CODING_STYLE files.
Additional information on submitting patches can be found online via
the QEMU website
https://qemu.org/Contribute/SubmitAPatch
https://qemu.org/Contribute/TrivialPatches
The QEMU website is also maintained under source control.
git clone git://git.qemu.org/qemu-web.git
https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/
Bug reporting
=============
The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs
found when running code built from QEMU git or upstream released sources
should be reported via:
https://bugs.launchpad.net/qemu/
If using QEMU via an operating system vendor pre-built binary package, it
is preferable to report bugs to the vendor's own bug tracker first. If
the bug is also known to affect latest upstream code, it can also be
reported via launchpad.
For additional information on bug reporting consult:
https://qemu.org/Contribute/ReportABug
Contact
=======
The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC
- qemu-devel@nongnu.org
https://lists.nongnu.org/mailman/listinfo/qemu-devel
- #qemu on irc.oftc.net
Information on additional methods of contacting the community can be
found online via the QEMU website:
https://qemu.org/Contribute/StartHere
-- End