linux-kernel - RE: [PATCH v5 28/34] x86/fred: fixup fault on ERETU by jumping to fred_entrypoint

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Date:   Sat, 18 Mar 2023 07:55:08 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v5 28/34] x86/fred: fixup fault on ERETU by jumping to
 fred_entrypoint_user

> > +#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?