diff options
author | Andy Lutomirski <luto@kernel.org> | 2017-10-14 09:59:50 -0700 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2017-10-18 15:25:02 +0200 |
commit | 4e57b94664fef55aa71cac33b4632fdfdd52b695 (patch) | |
tree | e1d26524e19b53b33f6dc38942b0f0e9ea645256 /arch/x86 | |
parent | e8b9b0cc8269c85d8167aaee024bfcbb4976c031 (diff) |
x86/mm: Tidy up "x86/mm: Flush more aggressively in lazy TLB mode"
Due to timezones, commit:
b956575bed91 ("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was an outdated patch that well tested and fixed the bug but didn't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: Borislav Petkov <bp@alien8.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: b956575bed91 ("x86/mm: Flush more aggressively in lazy TLB mode")
Link: http://lkml.kernel.org/r/154ef95428d4592596b6e98b0af1d2747d6cfbf8.1508000261.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86')
-rw-r--r-- | arch/x86/include/asm/tlbflush.h | 7 | ||||
-rw-r--r-- | arch/x86/mm/tlb.c | 30 |
2 files changed, 24 insertions, 13 deletions
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index d362161d3291..0d4a1bb7e303 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -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 diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 7db23f9f804e..5ee3b59baa85 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -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); |