I am re-introducing the patchset for <acpi-hotplug-bridge> which got reverted here few months back: https://www.spinics.net/linux/fedora/libvir/msg224089.html The reason for the reversal was that there seemed to be some instability/issues around the use of the qemu commandline which this patchset tries to support. In particular, some guest operating systems did not like the way QEMU was trying to disable native hotplug on pcie root ports. Subsequently, in QEMU 6.2, we have changed our mechanism using which we disable native hotplug. As I understand, we do not have any reported issues so far in 6.2 around this area. QEMU will enter a soft feature freeze in the first week of march in prep for 7.0 release. Libvirt is also entering a new release cycle phaze. Hence, I am introducing this patchset early enough in the release cycles so that if we do see any issues on the qemu side during the rc0, rc1 cycles and if reversal of this patchset is again required, it can be done in time before the next libvirt release end of March. All the patches in this series had been previously reviewed. Some subsequent fixes were made after my initial patches were pushed. I have squashed all those fixes and consolidated them into four patches. I have also updated the documentation to reflect the new changes from the QEMU side and rebased my changes fixing the tests in the process. What changed in QEMU post version 6.1 ? ========================================= We have made basically two major changes in QEMU. First is this change: (1) commit 211afe5c69b597acf85fdd577eb497f5be1ffbd8 Author: Julia Suvorova <jusual(a)redhat.com&gt; Date: Fri Nov 12 06:08:56 2021 -0500 hw/i386/acpi-build: Deny control on PCIe Native Hot-plug in _OSC There are two ways to enable ACPI PCI Hot-plug: * Disable the Hot-plug Capable bit on PCIe slots. This was the first approach which led to regression [1-2], as I/O space for a port is allocated only when it is hot-pluggable, which is determined by HPC bit. * Leave the HPC bit on and disable PCIe Native Hot-plug in _OSC method. This removes the (future) ability of hot-plugging switches with PCIe Native hotplug since ACPI PCI Hot-plug only works with cold-plugged bridges. If the user wants to explicitely use this feature, they can disable ACPI PCI Hot-plug with: --global ICH9-LPC.acpi-pci-hotplug-with-bridge-support=off Change the bit in _OSC method so that the OS selects ACPI PCI Hot-plug instead of PCIe Native. [1] https://gitlab.com/qemu-project/qemu/-/issues/641 [2] https://bugzilla.redhat.com/show_bug.cgi?id=2006409 Signed-off-by: Julia Suvorova <jusual(a)redhat.com&gt; Signed-off-by: Igor Mammedov <imammedo(a)redhat.com&gt; Message-Id: <20211112110857.3116853-5-imammedo(a)redhat.com&gt; Reviewed-by: Ani Sinha <ani(a)anisinha.ca&gt; Reviewed-by: Michael S. Tsirkin <mst(a)redhat.com&gt; Signed-off-by: Michael S. Tsirkin <mst(a)redhat.com&gt; The patch description says it all. Instead of masking out the HPC bit in pcie slots, we keep them turned on. Instead, we do not advertize native hotplug capability for PCIE using _OSC control method. See section 6.2.11 in ACPI spec 6.2. At the same time, we turn on ACPI hotplug for these slots so now the guest OS can select ACPI hotplug instead. The second change is introduction of a property with which we keep the existing behavior for pc-q35-6.1 machines. This means HPC bit is masked and ACPI hotplug is enabled by default for pcie root ports. The QEMU commit is: (2) commit c318bef76206c2ecb6016e8e68c4ac6ff9a4c8cb Author: Julia Suvorova <jusual(a)redhat.com&gt; Date: Fri Nov 12 06:08:54 2021 -0500 hw/acpi/ich9: Add compat prop to keep HPC bit set for 6.1 machine type To solve issues [1-2] the Hot Plug Capable bit in PCIe Slots will be turned on, while the switch to ACPI Hot-plug will be done in the DSDT table. Introducing 'x-keep-native-hpc' property disables the HPC bit only in 6.1 and as a result keeps the forced 'reserve-io' on pcie-root-ports in 6.1 too. [1] https://gitlab.com/qemu-project/qemu/-/issues/641 [2] https://bugzilla.redhat.com/show_bug.cgi?id=2006409 Signed-off-by: Julia Suvorova <jusual(a)redhat.com&gt; Signed-off-by: Igor Mammedov <imammedo(a)redhat.com&gt; Message-Id: <20211112110857.3116853-3-imammedo(a)redhat.com&gt; Reviewed-by: Michael S. Tsirkin <mst(a)redhat.com&gt; Signed-off-by: Michael S. Tsirkin <mst(a)redhat.com&gt; Lastly, as a related side note, because from QEMU 6.2 onwards, we do not mask out HPC bit in PCIE, the work done by this patch is no longer needed: (3) commit e2a6290aab578b2170c1f5909fa556385dc0d820 Author: Marcel Apfelbaum <marcel.apfelbaum(a)gmail.com&gt; Date: Mon Aug 2 12:00:57 2021 +0300 hw/pcie-root-port: Fix hotplug for PCI devices requiring IO Q35 has now ACPI hotplug enabled by default for PCI(e) devices. As opposed to native PCIe hotplug, guests like Fedora 34 will not assign IO range to pcie-root-ports not supporting native hotplug, resulting into a regression. Reproduce by: qemu-bin -M q35 -device pcie-root-port,id=p1 -monitor stdio device_add e1000,bus=p1 In the Guest OS the respective pcie-root-port will have the IO range disabled. Fix it by setting the "reserve-io" hint capability of the pcie-root-ports so the firmware will allocate the IO range instead. Acked-by: Igor Mammedov <imammedo(a)redhat.com&gt; Signed-off-by: Marcel Apfelbaum <marcel(a)redhat.com&gt; Message-Id: <20210802090057.1709775-1-marcel(a)redhat.com&gt; Reviewed-by: Michael S. Tsirkin <mst(a)redhat.com&gt; Signed-off-by: Michael S. Tsirkin <mst(a)redhat.com&gt; This is what commit (2) alludes to. In pc-q35-6.1 machines we do need patch (3) since we mask out HPC bit from pcie ports. I know this is convoluted mess. In fairness I am trying all I can in my spare time to help from the QEMU side. I am determined to see this patchset through into libvirt. Thanks Ani Sinha (4): qemu: capablities: detect acpi-pci-hotplug-with-bridge-support conf: introduce support for acpi-bridge-hotplug feature qemu: command: add support for acpi-bridge-hotplug feature NEWS: document new acpi pci hotplug config option NEWS.rst | 21 +++++ docs/formatdomain.rst | 32 +++++++ docs/schemas/domaincommon.rng | 15 ++++ src/conf/domain_conf.c | 89 ++++++++++++++++++- src/conf/domain_conf.h | 9 ++ src/qemu/qemu_capabilities.c | 4 + src/qemu/qemu_capabilities.h | 3 + src/qemu/qemu_command.c | 19 ++++ src/qemu/qemu_validate.c | 42 +++++++++ .../caps_6.1.0.x86_64.xml | 1 + .../caps_6.2.0.x86_64.xml | 1 + .../caps_7.0.0.x86_64.xml | 1 + ...-hotplug-bridge-disable.aarch64-latest.err | 1 + .../aarch64-acpi-hotplug-bridge-disable.xml | 13 +++ ...-hotplug-bridge-disable.x86_64-latest.args | 35 ++++++++ .../pc-i440fx-acpi-hotplug-bridge-disable.xml | 36 ++++++++ .../pc-i440fx-acpi-hotplug-bridge-enable.xml | 36 ++++++++ ...pi-hotplug-bridge-disable.x86_64-6.0.0.err | 1 + ...-hotplug-bridge-disable.x86_64-latest.args | 38 ++++++++ .../q35-acpi-hotplug-bridge-disable.xml | 53 +++++++++++ .../q35-acpi-hotplug-bridge-enable.xml | 53 +++++++++++ tests/qemuxml2argvtest.c | 7 ++ ...i-hotplug-bridge-disable.x86_64-latest.xml | 1 + ...pi-hotplug-bridge-enable.x86_64-latest.xml | 1 + ...i-hotplug-bridge-disable.x86_64-latest.xml | 1 + ...pi-hotplug-bridge-enable.x86_64-latest.xml | 1 + tests/qemuxml2xmltest.c | 4 + 27 files changed, 517 insertions(+), 1 deletion(-) create mode 100644 tests/qemuxml2argvdata/aarch64-acpi-hotplug-bridge-disable.aarch64-latest.err create mode 100644 tests/qemuxml2argvdata/aarch64-acpi-hotplug-bridge-disable.xml create mode 100644 tests/qemuxml2argvdata/pc-i440fx-acpi-hotplug-bridge-disable.x86_64-latest.args create mode 100644 tests/qemuxml2argvdata/pc-i440fx-acpi-hotplug-bridge-disable.xml create mode 100644 tests/qemuxml2argvdata/pc-i440fx-acpi-hotplug-bridge-enable.xml create mode 100644 tests/qemuxml2argvdata/q35-acpi-hotplug-bridge-disable.x86_64-6.0.0.err create mode 100644 tests/qemuxml2argvdata/q35-acpi-hotplug-bridge-disable.x86_64-latest.args create mode 100644 tests/qemuxml2argvdata/q35-acpi-hotplug-bridge-disable.xml create mode 100644 tests/qemuxml2argvdata/q35-acpi-hotplug-bridge-enable.xml create mode 120000 tests/qemuxml2xmloutdata/pc-i440fx-acpi-hotplug-bridge-disable.x86_64-latest.xml create mode 120000 tests/qemuxml2xmloutdata/pc-i440fx-acpi-hotplug-bridge-enable.x86_64-latest.xml create mode 120000 tests/qemuxml2xmloutdata/q35-acpi-hotplug-bridge-disable.x86_64-latest.xml create mode 120000 tests/qemuxml2xmloutdata/q35-acpi-hotplug-bridge-enable.x86_64-latest.xml -- 2.25.1