[libvirt] [PATCH RESEND v2 0/4] re-introduce <acpi-hotplug-bridge>
Michael S. Tsirkin
mst at redhat.com
Tue Mar 8 16:30:07 UTC 2022
On Tue, Mar 08, 2022 at 09:57:04PM +0530, Ani Sinha wrote:
>
>
> On Tue, Mar 8, 2022 at 21:21 Laine Stump <laine at redhat.com> wrote:
>
> Aha! the domain of qemu-devel at nongnu.org was incorrect in the original
> send (it was "nognu.org"), so none of this thread was making it to that
> list. I've corrected it in this message, but interested parties from
> qemu-devel will need to look on the libvir-list archives for the actual
> patch mails:
>
> https://listman.redhat.com/archives/libvir-list/2022-March/229089.html
>
> Anyone else who responds to any of the mail on this thread should fix
> the qemu-devel address accordingly.
>
>
> This patch set has been a true test of my diligence and perseverance 🙂
Right. But could you maybe repost to the proper qemu-devel?
I'd like to be able to pull the whole email not just the
summary listman deems safe to show me.
>
>
>
> On 3/8/22 10:33 AM, Laine Stump wrote:
> > On 3/8/22 1:39 AM, Ani Sinha wrote:
> >> Changelog:
> >> v2 - rebased the patch series to latest master.
> >>
> >> 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.
> >
> > 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 :-).
> >
> >> 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 at redhat.com>
> >> 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 at redhat.com>
> >> Signed-off-by: Igor Mammedov <imammedo at redhat.com>
> >> Message-Id: <20211112110857.3116853-5-imammedo at redhat.com>
> >> Reviewed-by: Ani Sinha <ani at anisinha.ca>
> >> Reviewed-by: Michael S. Tsirkin <mst at redhat.com>
> >> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> >>
> >>
> >> 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 at redhat.com>
> >> 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 at redhat.com>
> >> Signed-off-by: Igor Mammedov <imammedo at redhat.com>
> >> Message-Id: <20211112110857.3116853-3-imammedo at redhat.com>
> >> Reviewed-by: Michael S. Tsirkin <mst at redhat.com>
> >> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> >>
> >> 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 at gmail.com>
> >> 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 at redhat.com>
> >> Signed-off-by: Marcel Apfelbaum <marcel at redhat.com>
> >> Message-Id: <20210802090057.1709775-1-marcel at redhat.com>
> >> Reviewed-by: Michael S. Tsirkin <mst at redhat.com>
> >> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> >>
> >> 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 | 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
> >>
> >
>
>
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