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Subject: Re: [PATCH 12/30] x86, kaiser: map GDT into user page tables
References: <20171110193058.BECA7D88@viggo.jf.intel.com>
 <20171110193125.EBF58596@viggo.jf.intel.com>
 <alpine.DEB.2.20.1711202115190.2348@nanos>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <6f13e451-c333-d966-4169-ccda7a02ae06@linux.intel.com>
Date: Tue, 21 Nov 2017 14:12:40 -0800
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, luto@kernel.org, torvalds@linux-foundation.org, keescook@google.com, hughd@google.com, x86@kernel.org

On 11/20/2017 12:22 PM, Thomas Gleixner wrote:
> On Fri, 10 Nov 2017, Dave Hansen wrote:
>>  	__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
>> +
>> +	/* CPU 0's mapping is done in kaiser_init() */
>> +	if (cpu) {
>> +		int ret;
>> +
>> +		ret = kaiser_add_mapping((unsigned long) get_cpu_gdt_ro(cpu),
>> +					 PAGE_SIZE, __PAGE_KERNEL_RO);
>> +		/*
>> +		 * We do not have a good way to fail CPU bringup.
>> +		 * Just WARN about it and hope we boot far enough
>> +		 * to get a good log out.
>> +		 */
> 
> The GDT fixmap can be set up before the CPU is started. There is no reason
> to do that in cpu_init().

Do you mean the __set_fixmap(), or my call to kaiser_add_mapping()?

Where would you suggest we move it?  Here seems kinda nice because it's
right next to where the get_cpu_gdt_ro() mapping is created.

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