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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org
Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andi Kleen <ak@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Uros Bizjak <ubizjak@gmail.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Joerg Roedel <jroedel@suse.de>, Jian Cai <caij2003@gmail.com>
Subject: Re: [PATCH 2/4] x86/entry: Use asm_noist_exc_nmi() for NMI in early booting stage
In-Reply-To: <87bl9rk23k.ffs@nanos.tec.linutronix.de>
References: <20210426230949.3561-1-jiangshanlai@gmail.com> <20210426230949.3561-3-jiangshanlai@gmail.com> <87bl9rk23k.ffs@nanos.tec.linutronix.de>
Date:   Mon, 03 May 2021 22:24:18 +0200
Message-ID: <878s4vk1l9.ffs@nanos.tec.linutronix.de>
MIME-Version: 1.0
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On Mon, May 03 2021 at 22:13, Thomas Gleixner wrote:

> On Tue, Apr 27 2021 at 07:09, Lai Jiangshan wrote:
>> + *
>> + * While the other entries for the exceptions which use Interrupt stacks can
>> + * be also used on the kernel stack, asm_exc_nmi() can not be used on the
>> + * kernel stack for it relies on the RSP-located "NMI executing" variable
>> + * which expects to on a fixed location in the NMI IST stack.  For early
>> + * booting stage, asm_noist_exc_nmi() is used for NMI.
>>   */
>>  static const __initconst struct idt_data def_idts[] = {
>>  	INTG(X86_TRAP_DE,		asm_exc_divide_error),
>> -	INTG(X86_TRAP_NMI,		asm_exc_nmi),
>> +	INTG(X86_TRAP_NMI,		asm_noist_exc_nmi),
>
> Actually this is a x86_64 only problem. The 32bit variant is fine, but
> for consistency there is no problem to have that extra entry point on
> 32bit as well.

Bah, no. This patch breaks 32bit because on 32bit nothing sets the entry
to asm_exc_nmi() later on.

Thanks,

        tglx