Revert "x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation"

This reverts commit 66fe51cb35d91d75a67ec8a38caf03da95e8c191 which is
commit 53c613fe6349994f023245519265999eed75957f upstream.

It's not ready for the stable trees as there are major slowdowns
involved with this patch.

Reported-by: Jiri Kosina <jkosina@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc:  "WoodhouseDavid" <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc:  "SchauflerCasey" <casey.schaufler@intel.com>
Cc: Rainer Fiebig <jrf@mailbox.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 647a702c29dc12ed4e75def8c16dcc1afbbabb19..6221166e3fca546c3174d5ab8ad52ead2aada26b 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -33,10 +33,12 @@ static void __init spectre_v2_select_mitigation(void);
 static void __init ssb_select_mitigation(void);
 static void __init l1tf_select_mitigation(void);
 
-/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
-u64 x86_spec_ctrl_base;
+/*
+ * Our boot-time value of the SPEC_CTRL MSR. We read it once so that any
+ * writes to SPEC_CTRL contain whatever reserved bits have been set.
+ */
+u64 __ro_after_init x86_spec_ctrl_base;
 EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
-static DEFINE_MUTEX(spec_ctrl_mutex);
 
 /*
  * The vendor and possibly platform specific bits which can be modified in
@@ -320,46 +322,6 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
        return cmd;
 }
 
-static bool stibp_needed(void)
-{
-       if (spectre_v2_enabled == SPECTRE_V2_NONE)
-               return false;
-
-       if (!boot_cpu_has(X86_FEATURE_STIBP))
-               return false;
-
-       return true;
-}
-
-static void update_stibp_msr(void *info)
-{
-       wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
-}
-
-void arch_smt_update(void)
-{
-       u64 mask;
-
-       if (!stibp_needed())
-               return;
-
-       mutex_lock(&spec_ctrl_mutex);
-       mask = x86_spec_ctrl_base;
-       if (cpu_smt_control == CPU_SMT_ENABLED)
-               mask |= SPEC_CTRL_STIBP;
-       else
-               mask &= ~SPEC_CTRL_STIBP;
-
-       if (mask != x86_spec_ctrl_base) {
-               pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",
-                               cpu_smt_control == CPU_SMT_ENABLED ?
-                               "Enabling" : "Disabling");
-               x86_spec_ctrl_base = mask;
-               on_each_cpu(update_stibp_msr, NULL, 1);
-       }
-       mutex_unlock(&spec_ctrl_mutex);
-}
-
 static void __init spectre_v2_select_mitigation(void)
 {
        enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@@ -459,9 +421,6 @@ specv2_set_mode:
                setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
                pr_info("Enabling Restricted Speculation for firmware calls\n");
        }
-
-       /* Enable STIBP if appropriate */
-       arch_smt_update();
 }
 
 #undef pr_fmt
@@ -854,8 +813,6 @@ static ssize_t l1tf_show_state(char *buf)
 static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
                               char *buf, unsigned int bug)
 {
-       int ret;
-
        if (!boot_cpu_has_bug(bug))
                return sprintf(buf, "Not affected\n");
 
@@ -870,12 +827,10 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
                return sprintf(buf, "Mitigation: __user pointer sanitization\n");
 
        case X86_BUG_SPECTRE_V2:
-               ret = sprintf(buf, "%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
+               return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
                               boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "",
                               boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
-                              (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "",
                               spectre_v2_module_string());
-               return ret;
 
        case X86_BUG_SPEC_STORE_BYPASS:
                return sprintf(buf, "%s\n", ssb_strings[ssb_mode]);

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 8d7bace9a7b2a13ce10826e49a79ca3e20146006..b5a0165b7300c41f01a3366deea929a70d2c6f90 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1970,12 +1970,6 @@ static void cpuhp_online_cpu_device(unsigned int cpu)
        kobject_uevent(&dev->kobj, KOBJ_ONLINE);
 }
 
-/*
- * Architectures that need SMT-specific errata handling during SMT hotplug
- * should override this.
- */
-void __weak arch_smt_update(void) { };
-
 static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
 {
        int cpu, ret = 0;
@@ -2002,10 +1996,8 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
                 */
                cpuhp_offline_cpu_device(cpu);
        }
-       if (!ret) {
+       if (!ret)
                cpu_smt_control = ctrlval;
-               arch_smt_update();
-       }
        cpu_maps_update_done();
        return ret;
 }
@@ -2016,7 +2008,6 @@ static int cpuhp_smt_enable(void)
 
        cpu_maps_update_begin();
        cpu_smt_control = CPU_SMT_ENABLED;
-       arch_smt_update();
        for_each_present_cpu(cpu) {
                /* Skip online CPUs and CPUs on offline nodes */
                if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))