On 05.02.20 15:39, Stefan Hajnoczi wrote:
On Tue, Feb 04, 2020 at 12:30:42PM +0100, i.kotrasi...@partner.samsung.com
wrote:
From: Igor Kotrasinski <i.kotrasi...@partner.samsung.com>
This patchset adds a "memory exposing" device that allows two QEMU
instances to share arbitrary memory regions. Unlike ivshmem, it does not
create a new region of memory that's shared between VMs, but instead
allows one VM to access any memory region of the other VM we choose to
share.
The motivation for this device is a sort of ARM Trustzone "emulation",
where a rich system running on one machine (e.g. x86_64 linux) is able
to perform SMCs to a trusted system running on another (e.g. OpTEE on
ARM). With a device that allows sharing arbitrary memory between VMs,
this can be achieved with minimal changes to the trusted system and its
linux driver while allowing the rich system to run on a speedier x86
emulator. I prepared additional patches for linux, OpTEE OS and OpTEE
build system as a PoC that such emulation works and passes OpTEE tests;
I'm not sure what would be the best way to share them.
This patchset is my first foray into QEMU source code and I'm certain
it's not yet ready to be merged in. I'm not sure whether memory sharing
code has any race conditions or breaks rules of working with memory
regions, or if having VMs communicate synchronously via chardevs is the
right way to do it. I do believe the basic idea for sharing memory
regions is sound and that it could be useful for inter-VM communication.
Hi,
Without having looked into the patches yet, I'm already wondering if you
can use the existing -object
memory-backend-file,size=512M,mem-path=/my/shared/mem feature for your
use case?
That's the existing mechanism for fully sharing guest RAM and if you
want to share all of memory then maybe a device is not necessary - just
share the memory.
I suspect it's about sharing that memory in a discoverable way. Maybe it
is also about the signalling channel defined in the device.
OTOH, when it's really about sharing everything, even bidirectional,
that rather looks like a pragmatic shortcut, not a generic model.
The patches should clarify their use case a bit further, I think. The
title suggests a generic sharing solution, but my impression is that it
rather caters a specific case under specific boundary conditions.
Jan
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
