Re: [PATCH RESEND v2 0/4] re-introduce <acpi-hotplug-bridge>

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On Tue, Mar 08, 2022 at 09:57:04PM +0530, Ani Sinha wrote:
> 
> 
> On Tue, Mar 8, 2022 at 21:21 Laine Stump <laine@xxxxxxxxxx> wrote:
> 
>     Aha! the domain of qemu-devel@xxxxxxxxxx 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@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
>     >>
>     >>
>     >> 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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