> >> If there is no other concrete reason other than overflowing for assigning NMI > and > >> #DB with a stack level > 0, #VE should also be assigned with a stack level > 0, > and > >> #BP too. #VE can happen anytime and anywhere, so it is subject to > overflowing too. > > With IDT, both #VE and #BP do not use IST, but NMI, #DB, #MC and #DF do. > > > > Let's keep this "secret" logic for now, i.e., not change the stack levels > > for #VE and #BP at this point. We can do "optimization", i.e., change them > > later 😄. > > #VE also can't happen anywhere. There is some documentation about it in > here: > > https://docs.kernel.org/x86/tdx.html#linux-ve-handler > > But, basically, the only halfway sane thing a guest might do to hit a > #VE is touch some "MMIO". The host can *not* cause them in arbitrary > places because of the SEPT_VE_DISABLE attribute. > > #VE's also can't nest until after the guest retrieves the "VE info". > That means that the #VE handler at _least_ reaches C code before it's > subject to another #VE and that second one would still need to be > induced by something the guest does explicitly. Thanks a lot for the detailed background!
