On Thu, Jul 23, 2020 at 09:51:52AM +0100, Marc Zyngier wrote: > > IIRC on Intel/AMD at least once a MSI is launched it is not maskable. > > Really? So you can't shut a device with a screaming interrupt, > for example, should it become otherwise unresponsive? Well, it used to be like that in the APICv1 days. I suppose modern interrupt remapping probably changes things. > > So the model for MSI is always "mask at source". The closest mapping > > to the Linux IRQ model is to say the end device has a irqchip that > > encapsulates the ability of the device to generate the MSI in the > > first place. > > This is an x86'ism, I'm afraid. Systems I deal with can mask any > interrupt at the interrupt controller level, MSI or not. Sure. However it feels like a bad practice to leave the source unmasked and potentially continuing to generate messages if the intention was to disable the IRQ that was assigned to it - even if the messages do not result in CPU interrupts they will still consume system resources. > > I suppose the motivation to make it explicit is related to vfio using > > the generic mask/unmask functionality? > > > > Explicit seems better, IMHO. > > If masking at the source is the only way to shut the device up, > and assuming that the device provides the expected semantics > (a MSI raised by the device while the interrupt is masked > isn't lost and gets sent when unmasked), that's fair enough. > It's just ugly. It makes sense that the masking should follow the same semantics for PCI MSI masking. Jason
