> On Apr 25, 2020, at 12:10 PM, Joerg Roedel <joro@xxxxxxxxxx> wrote: > > On Sat, Apr 25, 2020 at 11:15:35AM -0700, Andy Lutomirski wrote: >> shift_ist is gross. What's it for? If it's not needed, I'd rather >> not use it, and I eventually want to get rid of it for #DB as well. > > The #VC handler needs to be able to nest, there is no way around that > for various reasons, the two most important ones are: > > 1. The #VC -> NMI -> #VC case. #VCs can happen in the NMI > handler, for example (but not exclusivly) for RDPMC. > > 2. In case of an error the #VC handler needs to print out error > information by calling one of the printk wrappers. Those will > end up doing IO to some console/serial port/whatever which > will also cause #VC exceptions to emulate the access to the > output devices. > > Using shift_ist is perfect for that, the only problem is the race > condition with the NMI handler, as shift_ist does not work well with > exceptions that can also trigger within the NMI handler. But I have > taken care of that for #VC. > I assume the race you mean is: #VC Immediate NMI before IST gets shifted #VC Kaboom. How are you dealing with this? Ultimately, I think that NMI will need to turn off IST before engaging in any funny business. Let me ponder this a bit. > > Regards, > > Joerg >
