On Wed, 11 Jun 2025 08:53:28 +0200
Eric Auger <eric.au...@redhat.com> wrote:
> Hi Gustavo, Alex,
>
> On 5/28/25 12:33 PM, Igor Mammedov wrote:
> > On Tue, 27 May 2025 15:54:15 +0200
> > Eric Auger <eric.au...@redhat.com> wrote:
> >
> >> Hi Igor,
> >>
> >> On 5/27/25 1:58 PM, Igor Mammedov wrote:
> >>> On Tue, 27 May 2025 09:40:04 +0200
> >>> Eric Auger <eric.au...@redhat.com> wrote:
> >>>
> >>>> acpi_pcihp VirtMachineClass state flag will allow
> >>>> to opt in for acpi pci hotplug. This is guarded by a
> >>>> class no_acpi_pcihp flag to manage compats (<= 10.0
> >>>> machine types will not support ACPI PCI hotplug).
> >>> there is no reason to put an effort in force disabling it
> >>> on old machines, as long as code works when explicitly
> >>> enabled property on CLI.
> >>>
> >>> See comment below on how to deal with it
> >>>
> >>>> Machine state acpi_pcihp flag must be set before the creation
> >>>> of the GED device which will use it.
> >>>>
> >>>> Currently the ACPI PCI HP is turned off by default. This will
> >>>> change later on for 10.1 machine type.
> >>> one thing to note, is that turning it on by default might
> >>> cause change of NIC naming in guest as this brings in
> >>> new "_Sxx" slot naming. /so configs tied to nic go down the drain/
> >>>
> >>> Naming, we have, also happens to be broken wrt spec
> >>> (it should be unique system wide, there was a gitlab issue for that,
> >>> there is no easy fix that though)
> >>>
> >>> So I'd leave it disabled by default and let users to turn
> >>> it on explicitly when needed.
> >> what is the status on q35, isn't it enabled by default? If so why
> >> wouldn't we want the same setting on ARM? Is that because of the known
> >> issue you report above?
> > Above issue is not a blocker (for thae lack of a good way to fix it)
> >
> > on q35 we have had a few complains and fixes, after pcihp was promoted
> > to default (so hopefully that won't happen on with ARM). Also given
> > that ARM VM is less popular like hood breaking someone setup is even less.
> >
> > That said I'd be cautions keep native hotplug as default,
> > and only ones who need ACPI one, could turn it on explicitly.
> >
> > But well it's policies, so it's up to you ARM folks to decide what
> > virt board should look like.
> What is your preference? Do you prefer enabling ACPI PCI HP by default
> or the opposite.
I'd prefer native PCIe hotplug being default,
that way we have less chance of causing regressions not to mention
less complexity (as acpi pcihp adds up quite a bit of it).
And ones who want/need acpi-pcihp/acpi-index can enable it explicitly,
to play with.
> Anybody else?
>
> On my end I think I would prefer to have the same default setting than
> on x86 (ie. ACPI PCI hotplug set by default) but I have no strong
> opinion either.
>
> Thanks
>
> Eric
> >
> >
> >> The no_foo compat stuff was especially introduced to avoid breaking the
> >> guest ABI for old machine types (like the NIC naming alternation you
> >> evoke).
> > no_foo is just another way to handle compat stuff,
> > and when it's more than one knob per feature it gets ugly really fast.
> > Hence, I'd prefer pcihp done in x86 way aka:
> > hw_compat_OLD(ged.use_acpi_hotplug_bridge, false|true)
> > to manage presence of ACPI hotplug on desired machine version.
> > Side benefit it's consistent with how pcihp works on x86
> >
> >>>
> >>>> We also introduce properties to allow disabling it.
> >>>>
> >>>> Signed-off-by: Eric Auger <eric.au...@redhat.com>
> >>>> Reviewed-by: Gustavo Romero <gustavo.rom...@linaro.org>
> >>>> ---
> >>>> include/hw/arm/virt.h | 2 ++
> >>>> hw/arm/virt.c | 27 +++++++++++++++++++++++++++
> >>>> 2 files changed, 29 insertions(+)
> >>>>
> >>>> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> >>>> index 9a1b0f53d2..10ea581f06 100644
> >>>> --- a/include/hw/arm/virt.h
> >>>> +++ b/include/hw/arm/virt.h
> >>>> @@ -129,6 +129,7 @@ struct VirtMachineClass {
> >>>> bool no_tcg_lpa2;
> >>>> bool no_ns_el2_virt_timer_irq;
> >>>> bool no_nested_smmu;
> >>>> + bool no_acpi_pcihp;
> >>>> };
> >>>>
> >>>> struct VirtMachineState {
> >>>> @@ -150,6 +151,7 @@ struct VirtMachineState {
> >>>> bool mte;
> >>>> bool dtb_randomness;
> >>>> bool second_ns_uart_present;
> >>>> + bool acpi_pcihp;
> >>>> OnOffAuto acpi;
> >>>> VirtGICType gic_version;
> >>>> VirtIOMMUType iommu;
> >>>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> >>>> index 9a6cd085a3..a0deeaf2b3 100644
> >>>> --- a/hw/arm/virt.c
> >>>> +++ b/hw/arm/virt.c
> >>>> @@ -2397,8 +2397,10 @@ static void machvirt_init(MachineState *machine)
> >>>> create_pcie(vms);
> >>>>
> >>>> if (has_ged && aarch64 && firmware_loaded &&
> >>>> virt_is_acpi_enabled(vms)) {
> >>>> + vms->acpi_pcihp &= !vmc->no_acpi_pcihp;
> >>> I don't particularly like no_foo naming as it makes code harder to read
> >>> and combined with 'duplicated' field in machine state it make even things
> >>> worse.
> >>> (if I recall right Philippe was cleaning mess similar flags usage
> >>> have introduced with ITS)
> >>>
> >>> instead of adding machine property (both class and state),
> >>> I'd suggest adding the only property to GPE device (akin to what we have
> >>> in x86 world)
> >>> And then one can meddle with defaults using hw_compat_xxx
> >> no_foo still is a largely used pattern in arm virt: no_ged,
> >> kvm_no_adjvtime, no_kvm_steal_time, no_tcg_lpa2, ../.. There are plenty
> >> of them and I am not under the impression this is going to be changed.
> >>
> >> If you refer to 8d23b1df7212 ("hw/arm/virt: Remove
> >> VirtMachineClass::no_its field") I think the no_its was removed because
> >> the machine it applied was removed.
> >>
> >> If I understand correctly you would like the prop to be attached to the
> >> GED device. However the GED device is internally created by the virt
> >> machine code and not passed through a "-device" CLI option. So how would
> >> you pass the option on the cmd line if you don't want it to be set by
> >> default per machine type?
> >>
> >> Thanks
> >>
> >> Eric
> >>>
> >>>> vms->acpi_dev = create_acpi_ged(vms);
> >>>> } else {
> >>>> + vms->acpi_pcihp = false;
> >>>> create_gpio_devices(vms, VIRT_GPIO, sysmem);
> >>>> }
> >>>>
> >>>> @@ -2593,6 +2595,20 @@ static void virt_set_its(Object *obj, bool value,
> >>>> Error **errp)
> >>>> vms->its = value;
> >>>> }
> >>>>
> >>>> +static bool virt_get_acpi_pcihp(Object *obj, Error **errp)
> >>>> +{
> >>>> + VirtMachineState *vms = VIRT_MACHINE(obj);
> >>>> +
> >>>> + return vms->acpi_pcihp;
> >>>> +}
> >>>> +
> >>>> +static void virt_set_acpi_pcihp(Object *obj, bool value, Error **errp)
> >>>> +{
> >>>> + VirtMachineState *vms = VIRT_MACHINE(obj);
> >>>> +
> >>>> + vms->acpi_pcihp = value;
> >>>> +}
> >>>> +
> >>>> static bool virt_get_dtb_randomness(Object *obj, Error **errp)
> >>>> {
> >>>> VirtMachineState *vms = VIRT_MACHINE(obj);
> >>>> @@ -3310,6 +3326,10 @@ static void virt_machine_class_init(ObjectClass
> >>>> *oc, const void *data)
> >>>> "in ACPI table header."
> >>>> "The string may be up to 8
> >>>> bytes in size");
> >>>>
> >>>> + object_class_property_add_bool(oc, "acpi-pcihp",
> >>>> + virt_get_acpi_pcihp,
> >>>> virt_set_acpi_pcihp);
> >>>> + object_class_property_set_description(oc, "acpi-pcihp",
> >>>> + "Force ACPI PCI hotplug");
> >>>> }
> >>>>
> >>>> static void virt_instance_init(Object *obj)
> >>>> @@ -3344,6 +3364,9 @@ static void virt_instance_init(Object *obj)
> >>>> vms->tcg_its = true;
> >>>> }
> >>>>
> >>>> + /* default disallows ACPI PCI hotplug */
> >>>> + vms->acpi_pcihp = false;
> >>>> +
> >>>> /* Default disallows iommu instantiation */
> >>>> vms->iommu = VIRT_IOMMU_NONE;
> >>>>
> >>>> @@ -3394,8 +3417,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(10, 1)
> >>>>
> >>>> static void virt_machine_10_0_options(MachineClass *mc)
> >>>> {
> >>>> + VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
> >>>> +
> >>>> virt_machine_10_1_options(mc);
> >>>> compat_props_add(mc->compat_props, hw_compat_10_0,
> >>>> hw_compat_10_0_len);
> >>>> + /* 10.0 and earlier do not support ACPI PCI hotplug */
> >>>> + vmc->no_acpi_pcihp = true;
> >>>> }
> >>>> DEFINE_VIRT_MACHINE(10, 0)
> >>>>
>
