linux-kernel - Re: [patch V2 35/44] x86/idt: Switch early trap init to IDT tables

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Message-ID: <alpine.DEB.2.20.1708261011001.2093@nanos>
Date:   Sat, 26 Aug 2017 10:16:43 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [patch V2 35/44] x86/idt: Switch early trap init to IDT tables

On Fri, 25 Aug 2017, Boris Ostrovsky wrote:
> On 08/25/2017 05:47 PM, Thomas Gleixner wrote:
> >  
> > -/* Set of traps needed for early debugging. */
> > -void __init early_trap_init(void)
> > -{
> > -	/*
> > -	 * Don't use IST to set DEBUG_STACK as it doesn't work until TSS
> > -	 * is ready in cpu_init() <-- trap_init(). Before trap_init(),
> > -	 * CPU runs at ring 0 so it is impossible to hit an invalid
> > -	 * stack.  Using the original stack works well enough at this
> > -	 * early stage. DEBUG_STACK will be equipped after cpu_init() in
> > -	 * trap_init().
> > -	 */
> > -	set_intr_gate(X86_TRAP_DB, debug);
> > -	/* int3 can be called from all */
> > -	set_system_intr_gate(X86_TRAP_BP, &int3);
> > -#ifdef CONFIG_X86_32
> > -	set_intr_gate(X86_TRAP_PF, page_fault);
> > -#endif
> > -	load_idt(&idt_descr);
> 
> This breaks 64-bit Xen PV guests: idt_setup_early_handler() is called
> from x86_64_start_kernel(), which is not executed on those guests.

early_trap_init() is called from setup_arch(), not from
x86_64_start_kernel().

This patch merily renames the function and moves the code into a different
source file. So it's not changing the behaviour in any way.

> The patch below fixes it.

I doubt that :)

Thanks,

	tglx

> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 03fb07d..ed0fb8a 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -1374,6 +1374,7 @@ asmlinkage __visible void __init
> xen_start_kernel(void)
>         i386_start_kernel();
>  #else
>         cr4_init_shadow(); /* 32b kernel does this in i386_start_kernel() */
> +       load_idt(&idt_descr);
>         x86_64_start_reservations((char *)__pa_symbol(&boot_params));
>  #endif
>  }