Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 4e57b946 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
Browse files

x86/mm: Tidy up "x86/mm: Flush more aggressively in lazy TLB mode" 



Due to timezones, commit:

  b956575b ("x86/mm: Flush more aggressively in lazy TLB mode")

was an outdated patch that well tested and fixed the bug but didn't
address Borislav's review comments.

Tidy it up:

 - The name "tlb_use_lazy_mode()" was highly confusing.  Change it to
   "tlb_defer_switch_to_init_mm()", which describes what it actually
   means.

 - Move the static_branch crap into a helper.

 - Improve comments.

Actually removing the debugfs option is in the next patch.

Reported-by: default avatarBorislav Petkov <bp@alien8.de>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: b956575b ("x86/mm: Flush more aggressively in lazy TLB mode")
Link: http://lkml.kernel.org/r/154ef95428d4592596b6e98b0af1d2747d6cfbf8.1508000261.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e8b9b0cc

arch/x86/include/asm/tlbflush.h

+6 −1
Original line number Diff line number Diff line
@@ -87,7 +87,12 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) 
 * to init_mm when we switch to a kernel thread (e.g. the idle thread).  If

 * it's false, then we immediately switch CR3 when entering a kernel thread.

 */

DECLARE_STATIC_KEY_TRUE(tlb_use_lazy_mode);

DECLARE_STATIC_KEY_TRUE(__tlb_defer_switch_to_init_mm);



static inline bool tlb_defer_switch_to_init_mm(void)

{

	return static_branch_unlikely(&__tlb_defer_switch_to_init_mm);

}



/*

 * 6 because 6 should be plenty and struct tlb_state will fit in

arch/x86/mm/tlb.c

+18 −12
Original line number Diff line number Diff line
@@ -30,7 +30,7 @@ 


atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);



DEFINE_STATIC_KEY_TRUE(tlb_use_lazy_mode);

DEFINE_STATIC_KEY_TRUE(__tlb_defer_switch_to_init_mm);



static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,

			    u16 *new_asid, bool *need_flush)
@@ -213,6 +213,9 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, 
}



/*

 * Please ignore the name of this function.  It should be called

 * switch_to_kernel_thread().

 *

 * enter_lazy_tlb() is a hint from the scheduler that we are entering a

 * kernel thread or other context without an mm.  Acceptable implementations

 * include doing nothing whatsoever, switching to init_mm, or various clever
@@ -227,7 +230,7 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) 
	if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm)

		return;



	if (static_branch_unlikely(&tlb_use_lazy_mode)) {

	if (tlb_defer_switch_to_init_mm()) {

		/*

		 * There's a significant optimization that may be possible

		 * here.  We have accurate enough TLB flush tracking that we
@@ -632,7 +635,8 @@ static ssize_t tlblazy_read_file(struct file *file, char __user *user_buf, 
{

	char buf[2];



	buf[0] = static_branch_likely(&tlb_use_lazy_mode) ? '1' : '0';

	buf[0] = static_branch_likely(&__tlb_defer_switch_to_init_mm)

		? '1' : '0';

	buf[1] = '\n';



	return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
@@ -647,9 +651,9 @@ static ssize_t tlblazy_write_file(struct file *file, 
		return -EINVAL;



	if (val)

		static_branch_enable(&tlb_use_lazy_mode);

		static_branch_enable(&__tlb_defer_switch_to_init_mm);

	else

		static_branch_disable(&tlb_use_lazy_mode);

		static_branch_disable(&__tlb_defer_switch_to_init_mm);



	return count;

}
@@ -660,23 +664,25 @@ static const struct file_operations fops_tlblazy = { 
	.llseek = default_llseek,

};



static int __init init_tlb_use_lazy_mode(void)

static int __init init_tlblazy(void)

{

	if (boot_cpu_has(X86_FEATURE_PCID)) {

		/*

		 * Heuristic: with PCID on, switching to and from

		 * init_mm is reasonably fast, but remote flush IPIs

		 * as expensive as ever, so turn off lazy TLB mode.

		 * If we have PCID, then switching to init_mm is reasonably

		 * fast.  If we don't have PCID, then switching to init_mm is

		 * quite slow, so we default to trying to defer it in the

		 * hopes that we can avoid it entirely.  The latter approach

		 * runs the risk of receiving otherwise unnecessary IPIs.

		 *

		 * We can't do this in setup_pcid() because static keys

		 * haven't been initialized yet, and it would blow up

		 * badly.

		 */

		static_branch_disable(&tlb_use_lazy_mode);

		static_branch_disable(&__tlb_defer_switch_to_init_mm);

	}



	debugfs_create_file("tlb_use_lazy_mode", S_IRUSR | S_IWUSR,

	debugfs_create_file("tlb_defer_switch_to_init_mm", S_IRUSR | S_IWUSR,

			    arch_debugfs_dir, NULL, &fops_tlblazy);

	return 0;

}

late_initcall(init_tlb_use_lazy_mode);
 
late_initcall(init_tlblazy);