From: Andy Lutomirski <luto@kernel.org>
Date: Sat, 14 Oct 2017 09:59:51 -0700
Subject: x86/mm: Remove debug/x86/tlb_defer_switch_to_init_mm
Git-commit: 7ac7f2c315ef76437f5119df354d334448534fb5
Patch-mainline: v4.14-rc6
References: bsc#1068032 CVE-2017-5754
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>
Acked-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/tlbflush.h | 20 ++++++++-----
arch/x86/mm/tlb.c | 58 ----------------------------------------
2 files changed, 12 insertions(+), 66 deletions(-)
--- 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
#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);
}
/*
--- 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)
@@ -665,60 +664,3 @@ static int __init create_tlb_single_page
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);