x86/mm: Remove debug/x86/tlb_defer_switch_to_init_mm

Borislav thinks that we don't need this knob in a released kernel.
Get rid of it.

Requested-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/1fa72431924e81e86c164ff7881bf9240d1f1a6c.1508000261.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 0d4a1bb7e303d0b71a210c101d4eebfa08764b32..c4aed0de565ed891283b6e214069b2611374947e 100644 (file)
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -82,16 +82,20 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
 #define __flush_tlb_single(addr) __native_flush_tlb_single(addr)
 #endif
 
-/*
- * If tlb_use_lazy_mode is true, then we try to avoid switching CR3 to point
- * 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_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);
+       /*
+        * 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 try to defer it in the hopes that we can
+        * avoid it entirely.  The latter approach runs the risk of
+        * receiving otherwise unnecessary IPIs.
+        *
+        * This choice is just a heuristic.  The tlb code can handle this
+        * function returning true or false regardless of whether we have
+        * PCID.
+        */
+       return !static_cpu_has(X86_FEATURE_PCID);
 }
 
 /*

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 5ee3b59baa85b16b5e38c26fba8e684237cf807a..0f3d0cea4d00ca253ee5b46ed78158d460797a56 100644 (file)
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -30,7 +30,6 @@
 
 atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);
 
-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)
@@ -629,60 +628,3 @@ static int __init create_tlb_single_page_flush_ceiling(void)
        return 0;
 }
 late_initcall(create_tlb_single_page_flush_ceiling);
-
-static ssize_t tlblazy_read_file(struct file *file, char __user *user_buf,
-                                size_t count, loff_t *ppos)
-{
-       char buf[2];
-
-       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);
-}
-
-static ssize_t tlblazy_write_file(struct file *file,
-                const char __user *user_buf, size_t count, loff_t *ppos)
-{
-       bool val;
-
-       if (kstrtobool_from_user(user_buf, count, &val))
-               return -EINVAL;
-
-       if (val)
-               static_branch_enable(&__tlb_defer_switch_to_init_mm);
-       else
-               static_branch_disable(&__tlb_defer_switch_to_init_mm);
-
-       return count;
-}
-
-static const struct file_operations fops_tlblazy = {
-       .read = tlblazy_read_file,
-       .write = tlblazy_write_file,
-       .llseek = default_llseek,
-};
-
-static int __init init_tlblazy(void)
-{
-       if (boot_cpu_has(X86_FEATURE_PCID)) {
-               /*
-                * 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_defer_switch_to_init_mm);
-       }
-
-       debugfs_create_file("tlb_defer_switch_to_init_mm", S_IRUSR | S_IWUSR,
-                           arch_debugfs_dir, NULL, &fops_tlblazy);
-       return 0;
-}
-late_initcall(init_tlblazy);