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id = 703
title = "Resizable BAR (ReBAR) support on VFIO"
state = "opened"
created_at = "2021-11-01T09:20:09.204Z"
closed_at = "n/a"
labels = ["VFIO", "kind::Feature Request"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/703"
host-os = "n/a"
host-arch = "n/a"
qemu-version = "n/a"
guest-os = "n/a"
guest-arch = "n/a"
description = "n/a"
reproduce = "n/a"
additional = """Currently `vfio_add_ext_cap()` doesn't pass ReBAR support option to VFIO.
There was a report that removing the line you see below makes it boot, but the system is not stable.
Needs investigation.
[https://github.com/qemu/qemu/blob/2255564fd21059960966b47212def9069cb56077/hw/vfio/pci.c#L2089](https://github.com/qemu/qemu/blob/2255564fd21059960966b47212def9069cb56077/hw/vfio/pci.c#L2089)
``` switch (cap_id) {
case 0: /* kernel masked capability */
case PCI_EXT_CAP_ID_SRIOV: /* Read-only VF BARs confuse OVMF */
case PCI_EXT_CAP_ID_ARI: /* XXX Needs next function virtualization */
case PCI_EXT_CAP_ID_REBAR: /* Can't expose read-only */
trace_vfio_add_ext_cap_dropped(vdev->vbasedev.name, cap_id, next);
```
[Discussion link](https://forum.level1techs.com/t/smart-access-memory-vs-qemu-kvm/169447)"""
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