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device: 0.933
graphic: 0.860
network: 0.811
VMM: 0.739
kernel: 0.728
vnc: 0.707
PID: 0.693
arm: 0.692
ppc: 0.684
risc-v: 0.665
register: 0.664
socket: 0.622
architecture: 0.620
semantic: 0.577
peripherals: 0.542
boot: 0.499
performance: 0.474
TCG: 0.463
permissions: 0.429
x86: 0.426
mistranslation: 0.402
i386: 0.387
debug: 0.384
files: 0.353
virtual: 0.337
assembly: 0.332
hypervisor: 0.280
KVM: 0.199
user-level: 0.151
Default machine setting of force-legacy=true causes problems for any modern VirtIO device using MMIO
Description of problem:
The default causes problems if you enable any non-legacy VirtIO device which has the VIRTIO_F_VERSION_1 feature bit will not properly read all feature bits. This is because reading VIRTIO_MMIO_VERSION returns VIRT_VERSION_LEGACY which in turn results in the driver not reading all feature bits, e.g. the qtest access:
```
static uint64_t qvirtio_mmio_get_features(QVirtioDevice *d)
{
QVirtioMMIODevice *dev = container_of(d, QVirtioMMIODevice, vdev);
uint64_t lo;
uint64_t hi = 0;
qtest_writel(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES_SEL, 0);
lo = qtest_readl(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES);
if (dev->version >= 2) {
qtest_writel(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES_SEL, 1);
hi = qtest_readl(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES);
}
return (hi << 32) | lo;
}
```
Additional information:
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