Commit 20bb8344 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
Browse files

x86/entry/64: Stop initializing TSS.sp0 at boot 



In my quest to get rid of thread_struct::sp0, I want to clean up or
remove all of its readers.  Two of them are in cpu_init() (32-bit and
64-bit), and they aren't needed.  This is because we never enter
userspace at all on the threads that CPUs are initialized in.

Poison the initial TSS.sp0 and stop initializing it on CPU init.

The comment text mostly comes from Dave Hansen.  Thanks!

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/ee4a00540ad28c6cff475fbcc7769a4460acc861.1509609304.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent f16b3da1

arch/x86/kernel/cpu/common.c

+10 −3
Original line number Diff line number Diff line
@@ -1570,9 +1570,13 @@ void cpu_init(void) 
	initialize_tlbstate_and_flush();

	enter_lazy_tlb(&init_mm, me);



	load_sp0(current->thread.sp0);

	/*

	 * Initialize the TSS.  Don't bother initializing sp0, as the initial

	 * task never enters user mode.

	 */

	set_tss_desc(cpu, t);

	load_TR_desc();



	load_mm_ldt(&init_mm);



	clear_all_debug_regs();
@@ -1594,7 +1598,6 @@ void cpu_init(void) 
	int cpu = smp_processor_id();

	struct task_struct *curr = current;

	struct tss_struct *t = &per_cpu(cpu_tss, cpu);

	struct thread_struct *thread = &curr->thread;



	wait_for_master_cpu(cpu);
@@ -1625,9 +1628,13 @@ void cpu_init(void) 
	initialize_tlbstate_and_flush();

	enter_lazy_tlb(&init_mm, curr);



	load_sp0(thread->sp0);

	/*

	 * Initialize the TSS.  Don't bother initializing sp0, as the initial

	 * task never enters user mode.

	 */

	set_tss_desc(cpu, t);

	load_TR_desc();



	load_mm_ldt(&init_mm);



	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);

arch/x86/kernel/process.c

+7 −1
Original line number Diff line number Diff line
@@ -48,7 +48,13 @@ 
 */

__visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {

	.x86_tss = {

		.sp0 = TOP_OF_INIT_STACK,

		/*

		 * .sp0 is only used when entering ring 0 from a lower

		 * privilege level.  Since the init task never runs anything

		 * but ring 0 code, there is no need for a valid value here.

		 * Poison it.

		 */

		.sp0 = (1UL << (BITS_PER_LONG-1)) + 1,

#ifdef CONFIG_X86_32

		.ss0 = __KERNEL_DS,

		.ss1 = __KERNEL_CS,

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