x86/topology: Add topology_max_smt_threads()

For SMT specific workarounds it is useful to know if SMT is active
on any online CPU in the system. This currently requires a loop
over all online CPUs.

Add a global variable that is updated with the maximum number
of smt threads on any CPU on online/offline, and use it for
topology_max_smt_threads()

The single call is easier to use than a loop.

Not exported to user space because user space already can use
the existing sibling interfaces to find this out.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Cc: jolsa@kernel.org
Link: http://lkml.kernel.org/r/1463703002-19686-2-git-send-email-andi@firstfloor.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

CVE-2018-3620
CVE-2018-3646

(cherry picked from commit 70b8301f)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/x86/include/asm/topology.h

@@ -130,6 +130,14 @@ extern const struct cpumask *cpu_coregroup_mask(int cpu);
 
 extern unsigned int __max_logical_packages;
 #define topology_max_packages()			(__max_logical_packages)
+
+extern int __max_smt_threads;
+
+static inline int topology_max_smt_threads(void)
+{
+	return __max_smt_threads;
+}
+
 int topology_update_package_map(unsigned int apicid, unsigned int cpu);
 int topology_phys_to_logical_pkg(unsigned int pkg);
 bool topology_is_primary_thread(unsigned int cpu);
@@ -139,6 +147,7 @@ bool topology_smt_supported(void);
 static inline int
 topology_update_package_map(unsigned int apicid, unsigned int cpu) { return 0; }
 static inline int topology_phys_to_logical_pkg(unsigned int pkg) { return 0; }
+static inline int topology_max_smt_threads(void) { return 1; }
 static inline bool topology_is_primary_thread(unsigned int cpu) { return true; }
 static inline bool topology_smt_supported(void) { return false; }
 #endif

arch/x86/kernel/smpboot.c

@@ -108,6 +108,9 @@ EXPORT_SYMBOL(__max_logical_packages);
 static unsigned int logical_packages __read_mostly;
 static bool logical_packages_frozen __read_mostly;
 
+/* Maximum number of SMT threads on any online core */
+int __max_smt_threads __read_mostly;
+
 static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
 {
 	unsigned long flags;
@@ -512,7 +515,7 @@ void set_cpu_sibling_map(int cpu)
 	bool has_mp = has_smt || boot_cpu_data.x86_max_cores > 1;
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
 	struct cpuinfo_x86 *o;
-	int i;
+	int i, threads;
 
 	cpumask_set_cpu(cpu, cpu_sibling_setup_mask);
 
@@ -569,6 +572,10 @@ void set_cpu_sibling_map(int cpu)
 		if (match_die(c, o) && !topology_same_node(c, o))
 			primarily_use_numa_for_topology();
 	}
+
+	threads = cpumask_weight(topology_sibling_cpumask(cpu));
+	if (threads > __max_smt_threads)
+		__max_smt_threads = threads;
 }
 
 /* maps the cpu to the sched domain representing multi-core */
@@ -1469,6 +1476,21 @@ __init void prefill_possible_map(void)
 
 #ifdef CONFIG_HOTPLUG_CPU
 
+/* Recompute SMT state for all CPUs on offline */
+static void recompute_smt_state(void)
+{
+	int max_threads, cpu;
+
+	max_threads = 0;
+	for_each_online_cpu (cpu) {
+		int threads = cpumask_weight(topology_sibling_cpumask(cpu));
+
+		if (threads > max_threads)
+			max_threads = threads;
+	}
+	__max_smt_threads = max_threads;
+}
+
 static void remove_siblinginfo(int cpu)
 {
 	int sibling;
@@ -1494,6 +1516,7 @@ static void remove_siblinginfo(int cpu)
 	c->cpu_core_id = 0;
 	c->booted_cores = 0;
 	cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
+	recompute_smt_state();
 }
 
 static void remove_cpu_from_maps(int cpu)