Merge branch 'for-linus' into for-next

* for-linus: (778 commits)
  ALSA: usb-audio - Fix invalid volume resolution on Logitech HD webcam c270
  ALSA: usb-audio - Apply Logitech QuickCam Pro 9000 quirk only to audio iface
  ALSA: hda/via - Clean up duplicated codes
  ALSA: hda/via - Fix wrongly cleared pins after suspend on VT1802
  ALSA: hda - Add keep_eapd_on flag to generic parser
  ALSA: hda - Allow setting automute/automic hooks after parsing
  ALSA: hda/via - Disable broken dynamic power control
  ALSA: usb-audio: fix Roland/Cakewalk UM-3G support
  ALSA: hda - Add headset quirk for two Dell machines
  ALSA: hda - add dock support for Thinkpad T431s
  ALSA: sis7019: fix error return code in sis_chip_create()
  ASoC: cs42l52: fix default value for MASTERA_VOL.
  ASoC: wm8994: check for array index returned
  ASoC: wm8994: Fix reporting of accessory removal on WM8958
  ASoC: wm8994: use the correct pointer to get the control value
  Linux 3.10-rc3
  ipc/sem.c: Fix missing wakeups in do_smart_update_queue()
  score: remove redundant kcore_list entries
  ASoC: wm5110: Correct DSP4R Mixer control name
  ARC: lazy dcache flush broke gdb in non-aliasing configs
  ...

1 files changed, 18 insertions, 1 deletions

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);