x86/split_lock: Rework the initialization flow of split lock detection

[platform/kernel/linux-rpi.git] / arch / x86 / kernel / cpu / intel.c

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index db3e745..0c859c9 100644 (file)
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -44,7 +44,7 @@ enum split_lock_detect_state {
  * split_lock_setup() will switch this to sld_warn on systems that support
  * split lock detect, unless there is a command line override.
  */
-static enum split_lock_detect_state sld_state = sld_off;
+static enum split_lock_detect_state sld_state __ro_after_init = sld_off;
 
 /*
  * Processors which have self-snooping capability can handle conflicting
@@ -984,78 +984,87 @@ static inline bool match_option(const char *arg, int arglen, const char *opt)
        return len == arglen && !strncmp(arg, opt, len);
 }
 
+static bool split_lock_verify_msr(bool on)
+{
+       u64 ctrl, tmp;
+
+       if (rdmsrl_safe(MSR_TEST_CTRL, &ctrl))
+               return false;
+       if (on)
+               ctrl |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
+       else
+               ctrl &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
+       if (wrmsrl_safe(MSR_TEST_CTRL, ctrl))
+               return false;
+       rdmsrl(MSR_TEST_CTRL, tmp);
+       return ctrl == tmp;
+}
+
 static void __init split_lock_setup(void)
 {
+       enum split_lock_detect_state state = sld_warn;
        char arg[20];
        int i, ret;
 
-       setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT);
-       sld_state = sld_warn;
+       if (!split_lock_verify_msr(false)) {
+               pr_info("MSR access failed: Disabled\n");
+               return;
+       }
 
        ret = cmdline_find_option(boot_command_line, "split_lock_detect",
                                  arg, sizeof(arg));
        if (ret >= 0) {
                for (i = 0; i < ARRAY_SIZE(sld_options); i++) {
                        if (match_option(arg, ret, sld_options[i].option)) {
-                               sld_state = sld_options[i].state;
+                               state = sld_options[i].state;
                                break;
                        }
                }
        }
 
-       switch (sld_state) {
+       switch (state) {
        case sld_off:
                pr_info("disabled\n");
-               break;
-
+               return;
        case sld_warn:
                pr_info("warning about user-space split_locks\n");
                break;
-
        case sld_fatal:
                pr_info("sending SIGBUS on user-space split_locks\n");
                break;
        }
+
+       if (!split_lock_verify_msr(true)) {
+               pr_info("MSR access failed: Disabled\n");
+               return;
+       }
+
+       sld_state = state;
+       setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT);
 }
 
 /*
- * Locking is not required at the moment because only bit 29 of this
- * MSR is implemented and locking would not prevent that the operation
- * of one thread is immediately undone by the sibling thread.
- * Use the "safe" versions of rdmsr/wrmsr here because although code
- * checks CPUID and MSR bits to make sure the TEST_CTRL MSR should
- * exist, there may be glitches in virtualization that leave a guest
- * with an incorrect view of real h/w capabilities.
+ * MSR_TEST_CTRL is per core, but we treat it like a per CPU MSR. Locking
+ * is not implemented as one thread could undo the setting of the other
+ * thread immediately after dropping the lock anyway.
  */
-static bool __sld_msr_set(bool on)
+static void sld_update_msr(bool on)
 {
        u64 test_ctrl_val;
 
-       if (rdmsrl_safe(MSR_TEST_CTRL, &test_ctrl_val))
-               return false;
+       rdmsrl(MSR_TEST_CTRL, test_ctrl_val);
 
        if (on)
                test_ctrl_val |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
        else
                test_ctrl_val &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
 
-       return !wrmsrl_safe(MSR_TEST_CTRL, test_ctrl_val);
+       wrmsrl(MSR_TEST_CTRL, test_ctrl_val);
 }
 
 static void split_lock_init(void)
 {
-       if (sld_state == sld_off)
-               return;
-
-       if (__sld_msr_set(true))
-               return;
-
-       /*
-        * If this is anything other than the boot-cpu, you've done
-        * funny things and you get to keep whatever pieces.
-        */
-       pr_warn("MSR fail -- disabled\n");
-       sld_state = sld_off;
+       split_lock_verify_msr(sld_state != sld_off);
 }
 
 bool handle_user_split_lock(struct pt_regs *regs, long error_code)
@@ -1071,7 +1080,7 @@ bool handle_user_split_lock(struct pt_regs *regs, long error_code)
         * progress and set TIF_SLD so the detection is re-enabled via
         * switch_to_sld() when the task is scheduled out.
         */
-       __sld_msr_set(false);
+       sld_update_msr(false);
        set_tsk_thread_flag(current, TIF_SLD);
        return true;
 }
@@ -1085,7 +1094,7 @@ bool handle_user_split_lock(struct pt_regs *regs, long error_code)
  */
 void switch_to_sld(unsigned long tifn)
 {
-       __sld_msr_set(!(tifn & _TIF_SLD));
+       sld_update_msr(!(tifn & _TIF_SLD));
 }
 
 #define SPLIT_LOCK_CPU(model) {X86_VENDOR_INTEL, 6, model, X86_FEATURE_ANY}