On Tue, Mar 8, 2022 at 10:28 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Tue, Mar 08, 2022 at 10:15:49PM +0530, Ani Sinha wrote: > > > > Change log: > > v2: rebased the patchset. Laine's response is appended at the end. > > > > 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. > > Right. But unfortunately we did not yet really work on > a sane interface for this. Ok so are we going to do something about this? I am still very unclear as to what would be a sane interface both for i440fx and q35 (pci and pcie). > > The way I see it, at high level we thinkably need two flags > - disable ACPI hotplug > - enable native hotplug (maybe separately for pci and pcie?) > > and with both enabled guests actually can switch between > the two. > > This will at least reflect the hardware, so has a chance to be > stable. > > The big question however would be what is the actual use-case. > Without that this begs the question of why do we bother at all. > To allow hotplug of bridges? If it is really necessary for us then > we should think hard about questions that surround this: > > - how does one hotplug a pcie switch? > - any way to use e.g. dynamic ACPI to support hotplug of bridges? > - do we want to bite the bullet and create an option for management > to fully control guest memory layout including all pci devices? > > > > > 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@xxxxxxxxxx> > > 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@xxxxxxxxxx> > > Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx> > > Message-Id: <20211112110857.3116853-5-imammedo@xxxxxxxxxx> > > Reviewed-by: Ani Sinha <ani@xxxxxxxxxxx> > > Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > > > > 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@xxxxxxxxxx> > > 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@xxxxxxxxxx> > > Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx> > > Message-Id: <20211112110857.3116853-3-imammedo@xxxxxxxxxx> > > Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > > 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@xxxxxxxxx> > > 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@xxxxxxxxxx> > > Signed-off-by: Marcel Apfelbaum <marcel@xxxxxxxxxx> > > Message-Id: <20210802090057.1709775-1-marcel@xxxxxxxxxx> > > Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > > > > 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 > > > > Laine's comments ... > > > > My memory isn't completely clear, but I think there was also the issue > > that the option claims to enable ACPI hotplug when set to on, but > > instead what it actually does (in the Q35 case at least) is to enable > > native PCI hotplug when set to off (without actually disabling ACPI > > hotplug) and disable native PCI hotplug when set to on, or something > > like that. This ends up leaving it up to the guest OS to decide which > > type of hotplug to use, meaning its decision could override what's in > > the libvirt config, thus confusing everyone. Again, I probably have the > > details mixed up, but it was something like this. > > > > I asked mst about this this morning, and he suggested something that > > you've already done - Cc'ing the series to qemu-devel and the relevant > > maintainers so we can have a discussion with all involved parties about > > their opinions on whether we really should expose this existing option > > in libvirt, or if we should instead have two new options that are more > > orthogonal about enabling/disabling the two types of hotplug, so that > > libvirt config can more accurately represent what is being presented to > > the guest rather than a "best guess" of what we think the guest is going > > to do with what is presented. > > > > (Michael did also say that, with the current flurry of bug reports for > > the QEMU rc's, this discusion may not happen until closer to release > > when the bug reports die down. I know this doesn't mesh with your desire > > to "push now to allow for testing" (which in general would be a good > > thing if we were certain that we wanted the option like this and were > > just expecting some minor bugs that could be fixed), but my opinion is > > that 1) it's possible for anyone interested to test the functionality > > using <qemu:commandline>, and 2) we should avoid turning libvirt git > > into a revolving door of experiments. The only practical difference > > between using <qemu:commandline> and having a dedicated option is that > > the use of <qemu:commandline> causes the domain to be tainted, and the > > XML is a bit more complicated. But since the people we're talking about > > here will already have built their own libvirt binaries, the tainted > > status of any guests is irrelevant and the extra complexity of using > > <qemu:commandline> is probably trivial to them :-). > > > > > > 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 | 8 ++ > > 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, 504 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 >
