Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Thomas Gleixner:

 - Fix for a CPU hot-add deadlock in microcode update code

 - Fix for idle consolidation fallout

 - Documentation update for initial kernel direct mapping

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/mm: Add missing comments for initial kernel direct mapping
  x86/microcode: Add local mutex to fix physical CPU hot-add deadlock
  x86: Fix idle consolidation fallout

3 files changed, 23 insertions, 6 deletions

diff --git a/arch/x86/kernel/microcode_intel_early.c b/arch/x86/kernel/microcode_intel_early.c
index d893e8ed8ac9..2e9e12871c2b 100644
--- a/arch/x86/kernel/microcode_intel_early.c
+++ b/arch/x86/kernel/microcode_intel_early.c
@@ -487,6 +487,7 @@ static inline void show_saved_mc(void)
 #endif
 
 #if defined(CONFIG_MICROCODE_INTEL_EARLY) && defined(CONFIG_HOTPLUG_CPU)
+static DEFINE_MUTEX(x86_cpu_microcode_mutex);
 /*
  * Save this mc into mc_saved_data. So it will be loaded early when a CPU is
  * hot added or resumes.
@@ -507,7 +508,7 @@ int save_mc_for_early(u8 *mc)
          * Hold hotplug lock so mc_saved_data is not accessed by a CPU in
          * hotplug.
          */
-        cpu_hotplug_driver_lock();
+        mutex_lock(&x86_cpu_microcode_mutex);
 
         mc_saved_count_init = mc_saved_data.mc_saved_count;
         mc_saved_count = mc_saved_data.mc_saved_count;
@@ -544,7 +545,7 @@ int save_mc_for_early(u8 *mc)
         }
 
 out:
-        cpu_hotplug_driver_unlock();
+        mutex_unlock(&x86_cpu_microcode_mutex);
 
         return ret;
 }
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 607af0d4d5ef..4e7a37ff03ab 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -312,6 +312,8 @@ void arch_cpu_idle(void)
 {
         if (cpuidle_idle_call())
                 x86_idle();
+        else
+                local_irq_enable();
 }
 
 /*
@@ -368,9 +370,6 @@ void amd_e400_remove_cpu(int cpu)
  */
 static void amd_e400_idle(void)
 {
-        if (need_resched())
-                return;
-
         if (!amd_e400_c1e_detected) {
                 u32 lo, hi;
 
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index fdc5dca14fb3..eaac1743def7 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -359,7 +359,17 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 }
 
 /*
- * would have hole in the middle or ends, and only ram parts will be mapped.
+ * We need to iterate through the E820 memory map and create direct mappings
+ * for only E820_RAM and E820_KERN_RESERVED regions. We cannot simply
+ * create direct mappings for all pfns from [0 to max_low_pfn) and
+ * [4GB to max_pfn) because of possible memory holes in high addresses
+ * that cannot be marked as UC by fixed/variable range MTRRs.
+ * Depending on the alignment of E820 ranges, this may possibly result
+ * in using smaller size (i.e. 4K instead of 2M or 1G) page tables.
+ *
+ * init_mem_mapping() calls init_range_memory_mapping() with big range.
+ * That range would have hole in the middle or ends, and only ram parts
+ * will be mapped in init_range_memory_mapping().
  */
 static unsigned long __init init_range_memory_mapping(
                                            unsigned long r_start,
@@ -419,6 +429,13 @@ void __init init_mem_mapping(void)
         max_pfn_mapped = 0; /* will get exact value next */
         min_pfn_mapped = real_end >> PAGE_SHIFT;
         last_start = start = real_end;
+
+        /*
+         * We start from the top (end of memory) and go to the bottom.
+         * The memblock_find_in_range() gets us a block of RAM from the
+         * end of RAM in [min_pfn_mapped, max_pfn_mapped) used as new pages
+         * for page table.
+         */
         while (last_start > ISA_END_ADDRESS) {
                 if (last_start > step_size) {
                         start = round_down(last_start - 1, step_size);