Hi Peter, On Tue, Jun 23, 2020 at 12:45:59PM +0200, Peter Zijlstra wrote: > On Tue, Jun 23, 2020 at 11:45:19AM +0200, Joerg Roedel wrote: > > Or maybe you have a better idea how to implement this, so I'd like to > > hear your opinion first before I spend too many days implementing > > something. > > OK, excuse my ignorance, but I'm not seeing how that IST shifting > nonsense would've helped in the first place. > > If I understand correctly the problem is: > > <#VC> > shift IST > <NMI> > ... does stuff > <#VC> # again, safe because the shift > > But what happens if you get the NMI before your IST adjustment? The v3 patchset implements an unconditional shift of the #VC IST entry in the NMI handler, before it can trigger a #VC exception. > Either way around we get to fix this up in NMI (and any other IST > exception that can happen while in #VC, hello #MC). And more complexity > there is the very last thing we need :-( Yes, in whatever way this gets implemented, it needs some fixup in the NMI handler. But that can happen in C code, so it does not make the assembly more complex, at least. > There's no way you can fix up the IDT without getting an NMI first. Not sure what you mean by this. > This entire exception model is fundamentally buggered :-/ Regards, Joerg
