On Mon, Dec 19, 2022 at 10:36:48PM -0800, Xin Li wrote: > + wrmsrl(MSR_IA32_FRED_STKLVLS, > + FRED_STKLVL(X86_TRAP_DB, 1) | > + FRED_STKLVL(X86_TRAP_NMI, 2) | > + FRED_STKLVL(X86_TRAP_MC, 2) | > + FRED_STKLVL(X86_TRAP_DF, 3)); > + > + /* The FRED equivalents to IST stacks... */ > + wrmsrl(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB)); > + wrmsrl(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI)); > + wrmsrl(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF)); Not quite.. IIRC fred only switches to another stack when the level of the exception is higher. Specifically, if we trigger #DB while inside #NMI we will not switch to the #DB stack (since 1 < 2). Now, as mentioned elsewhere, it all nests a lot saner, but stack exhaustion is still a thing, given the above, what happens when a #DB hits an #NMI which tickles a #VE or something? I don't think we've increased the exception stack size, but perhaps we should for FRED?
