Re: [RFC PATCH v3 0/7] Use ACPI PCI hot-plug for Q35

[Michael S. Tsirkin]

On Thu, Sep 24, 2020 at 11:30:00AM +0200, Igor Mammedov wrote:
> On Thu, 24 Sep 2020 09:00:06 +0200
> Julia Suvorova <jusual@redhat.com> wrote:
> 
> > The patch set consists of two parts:
> > patches 1-4: introduce new feature
> >              'acpi-pci-hotplug-with-bridge-support' on Q35
> > patches 5-7: make the feature default along with changes in ACPI tables
> > 
> > This way maintainers can decide which way to choose without breaking
> > the patch set.
> > 
> > With the feature disabled Q35 falls back to the native hot-plug.
> > 
> > Pros
> >     * no racy behavior during boot (see 110c477c2ed)
> >     * eject is possible - according to PCIe spec, attention button
> >       press should lead to power off, and then the adapter should be
> >       removed manually. As there is no power down state exists in QEMU,
> >       we cannot distinguish between an eject and a power down
> >       request.
> 
> if I recall right, you had a idea about
>  keeping pending removal request to distinguish between eject and poweroff
>  (i.e. eject if mgmt asked for removal and otherwise it could be poweroff|nop)
>  Why it didn't work out in the end?

For better or worse guests expect to eject and have it happen,
without also asking management to do it ...

> >     * no delay during deleting - after the actual power off software
> >       must wait at least 1 second before indicating about it. This case
> >       is quite important for users, it even has its own bug:
> >           https://bugzilla.redhat.com/show_bug.cgi?id=1594168
> >     * no timer-based behavior - in addition to the previous example,
> >       the attention button has a 5-second waiting period, during which
> >       the operation can be canceled with a second press. While this
> >       looks fine for manual button control, automation will result in
> >       the need to queue or drop events, and the software receiving
> >       events in all sort of unspecified combinations of attention/power
> >       indicator states, which is racy and uppredictable.
> >     * fixes:
> >         * https://bugzilla.redhat.com/show_bug.cgi?id=1752465
> >         * https://bugzilla.redhat.com/show_bug.cgi?id=1690256
> > 
> > Cons:
> >     * lose per-port control over hot-plug (can be resolved)
> >     * no access to possible features presented in slot capabilities
> >       (this is only surprise removal AFAIK)
> > 
> > v3:
> >     * drop change of _OSC to allow SHPC on hotplugged bridges
> >     * use 'acpi-root-pci-hotplug'
> >     * add migration states [Igor]
> >     * minor style changes
> > 
> > v2:
> >     * new ioport range for acpiphp [Gerd]
> >     * drop find_pci_host() [Igor]
> >     * explain magic numbers in _OSC [Igor]
> >     * drop build_q35_pci_hotplug() wrapper [Igor]
> > 
> > Julia Suvorova (7):
> >   hw/acpi/pcihp: Enhance acpi_pcihp_disable_root_bus() to support Q35
> >   hw/i386/acpi-build: Add ACPI PCI hot-plug methods to Q35
> >   hw/pci/pcie: Do not initialize slot capability if acpihp is used
> >   hw/acpi/ich9: Enable ACPI PCI hot-plug
> >   bios-tables-test: Allow changes in DSDT ACPI tables
> >   hw/acpi/ich9: Set ACPI PCI hot-plug as default
> >   bios-tables-test: Update golden binaries
> > 
> >  hw/i386/acpi-build.h              |   7 ++++
> >  include/hw/acpi/ich9.h            |   5 +++
> >  include/hw/acpi/pcihp.h           |   3 +-
> >  hw/acpi/ich9.c                    |  67 ++++++++++++++++++++++++++++++
> >  hw/acpi/pcihp.c                   |  16 ++++---
> >  hw/acpi/piix4.c                   |   4 +-
> >  hw/i386/acpi-build.c              |  31 ++++++++------
> >  hw/i386/pc.c                      |   1 +
> >  hw/pci/pcie.c                     |  16 +++++++
> >  tests/data/acpi/q35/DSDT          | Bin 7678 -> 7950 bytes
> >  tests/data/acpi/q35/DSDT.acpihmat | Bin 9002 -> 9274 bytes
> >  tests/data/acpi/q35/DSDT.bridge   | Bin 7695 -> 9865 bytes
> >  tests/data/acpi/q35/DSDT.cphp     | Bin 8141 -> 8413 bytes
> >  tests/data/acpi/q35/DSDT.dimmpxm  | Bin 9331 -> 9603 bytes
> >  tests/data/acpi/q35/DSDT.ipmibt   | Bin 7753 -> 8025 bytes
> >  tests/data/acpi/q35/DSDT.memhp    | Bin 9037 -> 9309 bytes
> >  tests/data/acpi/q35/DSDT.mmio64   | Bin 8808 -> 9080 bytes
> >  tests/data/acpi/q35/DSDT.numamem  | Bin 7684 -> 7956 bytes
> >  tests/data/acpi/q35/DSDT.tis      | Bin 8283 -> 8555 bytes
> >  19 files changed, 129 insertions(+), 21 deletions(-)
> >