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Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready |
Date: |
Thu, 22 Oct 2020 11:01:04 -0400 |
On Thu, Oct 22, 2020 at 05:50:51PM +0300, Marcel Apfelbaum wrote:
>
>
> On Thu, Oct 22, 2020 at 5:33 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Thu, Oct 22, 2020 at 05:10:43PM +0300, Marcel Apfelbaum wrote:
> >
> >
> > On Thu, Oct 22, 2020 at 5:01 PM Michael S. Tsirkin <mst@redhat.com>
> wrote:
> >
> >Â Â Â On Thu, Oct 22, 2020 at 04:55:10PM +0300, Marcel Apfelbaum wrote:
> >Â Â Â > Hi David, Michael,
> >Â Â Â >
> >Â Â Â > On Thu, Oct 22, 2020 at 3:56 PM David Gibson
> <dgibson@redhat.com>
> wrote:
> >Â Â Â >
> >Â Â Â >Â Â Â On Thu, 22 Oct 2020 08:06:55 -0400
> >Â Â Â >Â Â Â "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >Â Â Â >
> >Â Â Â >Â Â Â > On Thu, Oct 22, 2020 at 02:40:26PM +0300, Marcel
> Apfelbaum
> wrote:
> >Â Â Â >Â Â Â > > From: Marcel Apfelbaum <marcel@redhat.com>
> >Â Â Â >Â Â Â > >
> >Â Â Â >Â Â Â > > During PCIe Root Port's transition from Power-Off to
> Power-ON (or
> >Â Â Â >Â Â Â vice-versa)
> >Â Â Â >Â Â Â > > the "Slot Control Register" has the "Power Indicator
> Control"
> >Â Â Â >Â Â Â > > set to "Blinking" expressing a "power transition"
> mode.
> >Â Â Â >Â Â Â > >
> >Â Â Â >Â Â Â > > Any hotplug operation during the "power transition"
> mode is
> not
> >Â Â Â >Â Â Â permitted
> >Â Â Â >Â Â Â > > or at least not expected by the Guest OS leading to
> strange
> >Â Â Â failures.
> >Â Â Â >Â Â Â > >
> >Â Â Â >Â Â Â > > Detect and refuse hotplug operations in such case.
> >Â Â Â >Â Â Â > >
> >Â Â Â >Â Â Â > > Signed-off-by: Marcel Apfelbaum
> <marcel.apfelbaum@gmail.com
> >
> >Â Â Â >Â Â Â > > ---
> >Â Â Â >Â Â Â > >Â hw/pci/pcie.c | 7 +++++++
> >Â Â Â >Â Â Â > >Â 1 file changed, 7 insertions(+)
> >Â Â Â >Â Â Â > >
> >Â Â Â >Â Â Â > > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> >Â Â Â >Â Â Â > > index 5b48bae0f6..2fe5c1473f 100644
> >Â Â Â >Â Â Â > > --- a/hw/pci/pcie.c
> >Â Â Â >Â Â Â > > +++ b/hw/pci/pcie.c
> >Â Â Â >Â Â Â > > @@ -410,6 +410,7 @@ void pcie_cap_slot_pre_plug_cb
> (HotplugHandler
> >Â Â Â >Â Â Â *hotplug_dev, DeviceState *dev,
> >Â Â Â >Â Â Â > >Â Â Â PCIDevice *hotplug_pdev =
> PCI_DEVICE(hotplug_dev);
> >Â Â Â >Â Â Â > >Â Â Â uint8_t *exp_cap = hotplug_pdev->config +
> hotplug_pdev->
> >Â Â Â >Â Â Â exp.exp_cap;
> >Â Â Â >Â Â Â > >Â Â Â uint32_t sltcap = pci_get_word(exp_cap +
> PCI_EXP_SLTCAP);
> >Â Â Â >Â Â Â > > +Â Â uint32_t sltctl = pci_get_word(exp_cap +
> PCI_EXP_SLTCTL);
> >Â Â Â >Â Â Â > >Â
> >Â Â Â >Â Â Â > >Â Â Â /* Check if hot-plug is disabled on the
> slot */
> >Â Â Â >Â Â Â > >Â Â Â if (dev->hotplugged && (sltcap &
> PCI_EXP_SLTCAP_HPC) =
> = 0) {
> >Â Â Â >Â Â Â > > @@ -418,6 +419,12 @@ void pcie_cap_slot_pre_plug_cb
> >Â Â Â (HotplugHandler
> >Â Â Â >Â Â Â *hotplug_dev, DeviceState *dev,
> >Â Â Â >Â Â Â > >Â Â Â Â Â return;
> >Â Â Â >Â Â Â > >Â Â Â }
> >Â Â Â >Â Â Â > >Â
> >Â Â Â >Â Â Â > > +Â Â if ((sltctl & PCI_EXP_SLTCTL_PIC) ==
> >Â Â Â PCI_EXP_SLTCTL_PWR_IND_BLINK)
> >Â Â Â >Â Â Â {
> >Â Â Â >Â Â Â > > +Â Â Â Â error_setg(errp, "Hot-plug failed: %s
> is in Power
> >Â Â Â Transition",
> >Â Â Â >Â Â Â > > +Â Â Â Â Â Â Â Â Â Â
> DEVICE(hotplug_pdev)->id);
> >Â Â Â >Â Â Â > > +Â Â Â Â return;
> >Â Â Â >Â Â Â > > +Â Â }
> >Â Â Â >Â Â Â > > +
> >Â Â Â >Â Â Â > >Â Â Â
> pcie_cap_slot_plug_common(PCI_DEVICE(hotplug_dev),
> dev,
> >Â Â Â errp);
> >Â Â Â >Â Â Â > >Â }Â
> >Â Â Â >Â Â Â >
> >Â Â Â >Â Â Â > Probably the only way to handle for existing machine
> types.
> >Â Â Â >
> >Â Â Â >
> >Â Â Â > I agree
> >Â Â Â > Â
> >Â Â Â >
> >Â Â Â >Â Â Â > For new ones, can't we queue it in host memory
> somewhere?
> >Â Â Â >
> >Â Â Â >
> >Â Â Â >
> >Â Â Â > I am not sure I understand what will be the flow.
> >Â Â Â > Â - The user asks for a hotplug operation.
> >Â Â Â > Â -Â QEMU deferred operation.
> >Â Â Â > After that the operation may still fail, how would the user
> know if
> the
> >Â Â Â > operation
> >Â Â Â > succeeded or not?
> >
> >
> >Â Â Â How can it fail? It's just a button press ...
> >
> >
> >
> > Currently we have "Hotplug unsupported."
> > With this change we have "Guest/System not ready"
>
>
> Hotplug unsupported is not an error that can trigger with
> a well behaved management such as libvirt.
>
>
> > Â
> >
> >Â Â Â > Â
> >Â Â Â >
> >Â Â Â >Â Â Â I'm not actually convinced we can't do that even for
> existing
> machine
> >Â Â Â >Â Â Â types.Â
> >Â Â Â >
> >Â Â Â >
> >Â Â Â > Is a Guest visible change, I don't think we can do it.
> >Â Â Â > Â
> >Â Â Â >
> >Â Â Â >Â Â Â So I'm a bit hesitant to suggest going ahead with this
> without
> >Â Â Â >Â Â Â looking a bit closer at whether we can implement a
> wait-for-ready in
> >Â Â Â >Â Â Â qemu, rather than forcing every user of qemu (human or
> machine)
> to do
> >Â Â Â >Â Â Â so.
> >Â Â Â >
> >Â Â Â >
> >Â Â Â > While I agree it is a pain from the usability point of view,
> hotplug
> >Â Â Â operations
> >Â Â Â > are allowed to fail. This is not more than a corner case,
> ensuring
> the
> >Â Â Â right
> >Â Â Â > response (gracefully erroring out) may be enough.
> >Â Â Â >
> >Â Â Â > Thanks,
> >Â Â Â > Marcel
> >Â Â Â >
> >
> >
> >Â Â Â I don't think they ever failed in the past so management is
> unlikely
> >Â Â Â to handle the failure by retrying ...
> >
> >
> > That would require some management handling, yes.
> > But even without a "retry", failing is better than strange OS behavior.
> >
> > Trying a better alternative like deferring the operation for new
> machines
> > would make sense, however is out of the scope of this patch
>
> Expand the scope please. The scope should be "solve a problem xx" not
> "solve a problem xx by doing abc".
>
>
>
> The scope is detecting a hotplug error early instead
> passing to the Guest OS a hotplug operation that we know it will fail.
>
Right. After detecting just failing unconditionally it a bit too
simplistic IMHO.
>
> > that simply
> > detects the error leaving us in a slightly better state than today.
> >
> > Thanks,
> > Marcel
>
> Not applying a patch is the only tool we maintainers have to influence
> people to solve the problem fully.Â
>
> That's why I'm not inclined to apply
> "slightly better" patches generally.
>
>
>
> The patch is a proposal following some offline discussions on this matter.
> I personally see the value of it versus what we have today.
>
> Thanks,
> Marcel
>
>
> >
> >
> >Â Â Â >
> >Â Â Â >
> >Â Â Â >
> >Â Â Â >Â Â Â --
> >Â Â Â >Â Â Â David Gibson <dgibson@redhat.com>
> >Â Â Â >Â Â Â Principal Software Engineer, Virtualization, Red Hat
> >Â Â Â >
> >
> >
>
>
- [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Marcel Apfelbaum, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Michael S. Tsirkin, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, David Gibson, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Marcel Apfelbaum, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Michael S. Tsirkin, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Marcel Apfelbaum, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Michael S. Tsirkin, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Marcel Apfelbaum, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready,
Michael S. Tsirkin <=
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, David Gibson, 2020/10/22
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Marcel Apfelbaum, 2020/10/23
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Michael S. Tsirkin, 2020/10/23
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Igor Mammedov, 2020/10/23
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, David Gibson, 2020/10/26
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Peter Krempa, 2020/10/26
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, David Gibson, 2020/10/26
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Marcel Apfelbaum, 2020/10/23
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, David Gibson, 2020/10/26
- Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready, Michael S. Tsirkin, 2020/10/27