On Mon, Jul 19, 2021 at 8:51 AM Pali Rohár <pali@xxxxxxxxxx> wrote: > > And do we have some solution for this kind of issue? There are more PCIe > controllers / platforms which do not like MMIO read/write operation when > card / link is not connected. Do you have some actual examples? The few times I've seen those crashes were due to broken firmware-first error handling. The AER notifications would be escalated into some kind of ACPI error which the kernel didn't have a good way of dealing with so it panicked instead. Assuming it is a real problem then as Bjorn pointed out this sort of hack doesn't really fix the issue because hotplug and AER notifications are fundamentally asynchronous. If the driver is actively using the device when the error / removal happens then the pci_dev_is_disconnected() check will pass and the MMIO will go through. If the MMIO is poisonous because of dumb hardware then this sort of hack will only paper over the issue. > If we do not provide a way how to solve these problems then we can > expect that people would just hack ethernet / wifi / ... device drivers > which are currently crashing by patches like in this thread. > > Maybe PCI subsystem could provide wrapper function which implements > above pattern and which can be used by device drivers? We could do that and I think there was a proposal to add some pci_readl(pdev, <addr>) style wrappers at one point. On powerpc there's hooks in the arch provided MMIO functions to detect error responses and kick off the error handling machinery when a problem is detected. Those hooks are mainly there to help the platform detect errors though and they don't make life much easier for drivers. Due to locking concerns the driver's .error_detected() callback cannot be called in the MMIO hook so even when the platform detects errors synchronously the driver notifications must happen asynchronously. In the meanwhile the driver still needs to handle the 0xFFs response safely and there's not much we can do from the platform side to help there. Oliver
