RE: [PATCH v5 28/34] x86/fred: fixup fault on ERETU by jumping to fred_entrypoint_user

[Li, Xin3]

> > +#ifdef CONFIG_X86_FRED
> > +static bool ex_handler_eretu(const struct exception_table_entry *fixup,
> > +                            struct pt_regs *regs, unsigned long
> > +error_code) {
> > +       struct pt_regs *uregs = (struct pt_regs *)(regs->sp - offsetof(struct pt_regs,
> ip));
> > +       unsigned short ss = uregs->ss;
> > +       unsigned short cs = uregs->cs;
> > +
> > +       fred_info(uregs)->edata = fred_event_data(regs);
> > +       uregs->ssx = regs->ssx;
> > +       uregs->ss = ss;
> > +       uregs->csx = regs->csx;
> > +       uregs->current_stack_level = 0;
> > +       uregs->cs = cs;
> 
> Hello
> 
> If the ERETU instruction had tried to return from NMI to ring3 and just faulted, is
> NMI still blocked?

Do you mean the NMI FRED stack frame contains an invalid ring3 context?