x86/entry: Introduce local_db_{save,restore}()

In order to allow other exceptions than #DB to disable breakpoints,
provide common helpers.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200529213321.012060983@infradead.org

diff --git a/arch/x86/include/asm/debugreg.h b/arch/x86/include/asm/debugreg.h
index 1a8609a15856f6e02076f04324d06a803e3133c0..4ef8690be8a76ea7882d0d4f43fb2171beb44cd9 100644 (file)
--- a/arch/x86/include/asm/debugreg.h
+++ b/arch/x86/include/asm/debugreg.h
@@ -113,6 +113,36 @@ static inline void debug_stack_usage_inc(void) { }
 static inline void debug_stack_usage_dec(void) { }
 #endif /* X86_64 */
 
+static __always_inline unsigned long local_db_save(void)
+{
+       unsigned long dr7;
+
+       get_debugreg(dr7, 7);
+       dr7 &= ~0x400; /* architecturally set bit */
+       if (dr7)
+               set_debugreg(0, 7);
+       /*
+        * Ensure the compiler doesn't lower the above statements into
+        * the critical section; disabling breakpoints late would not
+        * be good.
+        */
+       barrier();
+
+       return dr7;
+}
+
+static __always_inline void local_db_restore(unsigned long dr7)
+{
+       /*
+        * Ensure the compiler doesn't raise this statement into
+        * the critical section; enabling breakpoints early would
+        * not be good.
+        */
+       barrier();
+       if (dr7)
+               set_debugreg(dr7, 7);
+}
+
 #ifdef CONFIG_CPU_SUP_AMD
 extern void set_dr_addr_mask(unsigned long mask, int dr);
 #else

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 50fb9cd5be97b030676cc05f1dbe04484289e653..bcb9dd961c6d6011930c0c8f6a801f6c6d768cf2 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -727,15 +727,7 @@ static __always_inline void debug_enter(unsigned long *dr6, unsigned long *dr7)
         * Entry text is excluded for HW_BP_X and cpu_entry_area, which
         * includes the entry stack is excluded for everything.
         */
-       get_debugreg(*dr7, 7);
-       set_debugreg(0, 7);
-
-       /*
-        * Ensure the compiler doesn't lower the above statements into
-        * the critical section; disabling breakpoints late would not
-        * be good.
-        */
-       barrier();
+       *dr7 = local_db_save();
 
        /*
         * The Intel SDM says:
@@ -756,13 +748,7 @@ static __always_inline void debug_enter(unsigned long *dr6, unsigned long *dr7)
 
 static __always_inline void debug_exit(unsigned long dr7)
 {
-       /*
-        * Ensure the compiler doesn't raise this statement into
-        * the critical section; enabling breakpoints early would
-        * not be good.
-        */
-       barrier();
-       set_debugreg(dr7, 7);
+       local_db_restore(dr7);
 }
 
 /*