linux-kernel - Re: [PATCH v7 67/72] x86/smpboot: Load TSS and getcpu GDT entry before loading IDT

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Date:   Tue, 8 Sep 2020 19:20:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, Joerg Roedel <jroedel@...e.de>, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Martin Radev <martin.b.radev@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v7 67/72] x86/smpboot: Load TSS and getcpu GDT entry
 before loading IDT

On Mon, Sep 07, 2020 at 03:16:08PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> The IDT on 64bit contains vectors which use paranoid_entry() and/or IST
> stacks. To make these vectors work the TSS and the getcpu GDT entry need
> to be set up before the IDT is loaded.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  arch/x86/include/asm/processor.h |  1 +
>  arch/x86/kernel/cpu/common.c     | 23 +++++++++++++++++++++++
>  arch/x86/kernel/smpboot.c        |  2 +-
>  3 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index d8a82e650810..5ac507586769 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -696,6 +696,7 @@ extern void load_direct_gdt(int);
>  extern void load_fixmap_gdt(int);
>  extern void load_percpu_segment(int);
>  extern void cpu_init(void);
> +extern void cpu_init_exception_handling(void);
>  extern void cr4_init(void);
>  
>  static inline unsigned long get_debugctlmsr(void)
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 1d65365363a1..a9527c0c38fb 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1854,6 +1854,29 @@ static inline void tss_setup_io_bitmap(struct tss_struct *tss)
>  #endif
>  }
>  
> +/*
> + * Setup everything needed to handle exceptions from the IDT, including the IST
> + * exceptions which use paranoid_entry()
> + */
> +void cpu_init_exception_handling(void)
> +{
> +	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
> +	int cpu = raw_smp_processor_id();
> +
> +	/* paranoid_entry() gets the CPU number from the GDT */
> +	setup_getcpu(cpu);
> +
> +	/* IST vectors need TSS to be set up. */
> +	tss_setup_ist(tss);
> +	tss_setup_io_bitmap(tss);
> +	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
> +
> +	load_TR_desc();

Aha, this is what you mean here in your 0th message. I'm guessing it is
ok to do those things twice in start_secondary...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette