On 18/7/26 20:44, Pierrick Bouvier wrote:
On 7/18/2026 4:51 AM, BALATON Zoltan wrote:
On Sat, 18 Jul 2026, Cédric Le Goater wrote:
On 7/18/26 06:52, Pierrick Bouvier wrote:
On 7/17/2026 9:14 PM, Michael Tokarev wrote:
On 7/17/26 22:40, Pierrick Bouvier wrote:
https://gitlab.com/qemu-project/qemu/-/blob/master/hw/vfio/Kconfig?
ref_type=heads#L5
```
config VFIO
bool
depends on LINUX
```
Incorrect, and it should exclude Linux hosts not supporting VFIO.
At least sparc64 to fix the current issue.
Shouldn't there be "depends on LINUX & KVM" ? At least, this
way we can do --disable-kvm and it will work.
I think it's a safe choice, but not sure if we are supposed to be able
to use the exotic combination of vfio with tcg also. Maybe it doesn't
make any sense technically though, I don't know the arcane of vfio.
VFIO works in some heterogeneous configurations, aarch64 TCG running
on an x86 host for instance. The opposite doesn't. ppc64 TCG on an x86
used to work. The limitations primarily stem from architectural
differences in the host/guest memory mode, CPU/IOMMU address spaces,
assumptions, etc.
@Cédric, Any idea of which matrix of host/target is supposed to be
supported?
>>> With KVM, the supported architectures are x86, aarch64, s390x, ppc64.
Overall, heterogeneous TCG configurations happen to work by accident.
I would not consider them supported.
VFIO (vfio-pci) works with PPC TCG and is used for passing through cards
including GPU to emulated AmigaNG machines (maybe also mac99).
So also Kconfig PPC (32-bit).
Can we assume the following is safe on 'LINUX && !KVM'?
#include <linux/kvm.h>
Please do
not break that. There are some quirks mostly with GPUs, see https://
qmiga.codeberg.page/qemu_vfio.html but it works and used by some people.
👍
In this case, and we want to ensure we don't break any existing workflow
we might now be aware of, a safe choice could be to restrict VFIO to all
hosts that supports KVM. This is different from CONFIG_KVM, which is
only enabled for new hosts.
@Michael: You'll need to detect kvm hosts (see meson.build for
kvm_targets), add a host config CONFIG_KVM_HOST, and use that for
CONFIG_VFIO definition. This should restrict VFIO to host providing KVM,
without limiting which target is ran.
For the 11.1 release I'd go with this 1-line fix:
- depends on LINUX
+ depends on LINUX && (AARCH64 || I386 || PPC || S390X)
Regards,
BALATON Zoltan
Regards,
Pierrick
