[+cc Rafael for question about ACPI method for PCI host bridge reset] On Sat, Nov 14, 2020 at 09:58:08PM +0100, Thomas Gleixner wrote: > On Sat, Nov 14 2020 at 14:39, Bjorn Helgaas wrote: > > On Sat, Nov 14, 2020 at 12:40:10AM +0100, Thomas Gleixner wrote: > >> On Sat, Nov 14 2020 at 00:31, Thomas Gleixner wrote: > >> > On Fri, Nov 13 2020 at 10:46, Bjorn Helgaas wrote: > >> >> pci_device_shutdown() still clears the Bus Master Enable bit if we're > >> >> doing a kexec and the device is in D0-D3hot, which should also disable > >> >> MSI/MSI-X. Why doesn't this solve the problem? Is this because the > >> >> device causing the storm was in PCI_UNKNOWN state? > >> > > >> > That's indeed a really good question. > >> > >> So we do that on kexec, but is that true when starting a kdump kernel > >> from a kernel crash? I doubt it. > > > > Ah, right, I bet that's it, thanks. The kdump path is basically this: > > > > crash_kexec > > machine_kexec > > > > while the usual kexec path is: > > > > kernel_kexec > > kernel_restart_prepare > > device_shutdown > > while (!list_empty(&devices_kset->list)) > > dev->bus->shutdown > > pci_device_shutdown # pci_bus_type.shutdown > > machine_kexec > > > > So maybe we need to explore doing some or all of device_shutdown() in > > the crash_kexec() path as well as in the kernel_kexec() path. > > The problem is that if the machine crashed anything you try to attempt > before starting the crash kernel is reducing the chance that the crash > kernel actually starts. Right. > Is there something at the root bridge level which allows to tell the > underlying busses to shut up, reset or go into a defined state? That > might avoid chasing lists which might be already unreliable. Maybe we need some kind of crash_device_shutdown() that does the minimal thing to protect the kdump kernel from devices. The programming model for conventional PCI host bridges and PCIe Root Complexes is device-specific since they're outside the PCI domain. There probably *are* ways to do those things, but you would need a native host bridge driver or something like an ACPI method. I'm not aware of an ACPI way to do this, but I added Rafael in case he is. A crash_device_shutdown() could do something at the host bridge level if that's possible, or reset/disable bus mastering/disable MSI/etc on individual PCI devices if necessary. Bjorn
