linux-kernel - Re: [PATCH 12/30] x86, kaiser: map GDT into user page tables

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Date:   Tue, 21 Nov 2017 14:12:40 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        luto@...nel.org, torvalds@...ux-foundation.org,
        keescook@...gle.com, hughd@...gle.com, x86@...nel.org
Subject: Re: [PATCH 12/30] x86, kaiser: map GDT into user page tables

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.