Bump up the maximum addressable memory on amd64 systems from 1TB to 4TB.

Bump up the KVA size proportionally from 512GB to 2TB.

The number of page table pages used by the direct map is now calculated at
run time based on 'Maxmem'. This means the small memory systems will not
see any additional tax in terms of page table pages for the direct map.

However all amd64 systems, regardless of the memory size, will use 3 more
pages to accomodate the bump in the KVA size.

More details available here:
http://lists.freebsd.org/pipermail/freebsd-hackers/2013-June/043015.html
http://lists.freebsd.org/pipermail/freebsd-current/2013-July/043143.html

Tested with the following configurations:
- Sandybridge server with 64GB of memory.
- bhyve VM with 64MB of memory.
- bhyve VM with a 8GB of memory with the memory segment above 4GB cuddling
  right up against the 4TB maximum memory limit.

Discussed on:	hackers@, current@
Submitted by:	Chris Torek (torek@torek.net)

2 files changed, 35 insertions, 13 deletions

diff --git a/sys/amd64/include/pmap.h b/sys/amd64/include/pmap.h
index ebe1780..46d126d 100644
--- a/sys/amd64/include/pmap.h
+++ b/sys/amd64/include/pmap.h
@@ -113,28 +113,49 @@
 	((unsigned long)(l2) << PDRSHIFT) | \
 	((unsigned long)(l1) << PAGE_SHIFT))
 
-#define NKPML4E		1		/* number of kernel PML4 slots */
+/*
+ * Number of kernel PML4 slots.  Can be anywhere from 1 to 64 or so,
+ * but setting it larger than NDMPML4E makes no sense.
+ *
+ * Each slot provides .5 TB of kernel virtual space.
+ */
+#define NKPML4E		4
 
 #define	NUPML4E		(NPML4EPG/2)	/* number of userland PML4 pages */
 #define	NUPDPE		(NUPML4E*NPDPEPG)/* number of userland PDP pages */
 #define	NUPDE		(NUPDPE*NPDEPG)	/* number of userland PD entries */
 
 /*
- * NDMPML4E is the number of PML4 entries that are used to implement the
- * direct map.  It must be a power of two.
+ * NDMPML4E is the maximum number of PML4 entries that will be
+ * used to implement the direct map.  It must be a power of two,
+ * and should generally exceed NKPML4E.  The maximum possible
+ * value is 64; using 128 will make the direct map intrude into
+ * the recursive page table map.
  */
-#define	NDMPML4E	2
+#define	NDMPML4E	8
 
 /*
- * The *PDI values control the layout of virtual memory.  The starting address
+ * These values control the layout of virtual memory.  The starting address
  * of the direct map, which is controlled by DMPML4I, must be a multiple of
  * its size.  (See the PHYS_TO_DMAP() and DMAP_TO_PHYS() macros.)
+ *
+ * Note: KPML4I is the index of the (single) level 4 page that maps
+ * the KVA that holds KERNBASE, while KPML4BASE is the index of the
+ * first level 4 page that maps VM_MIN_KERNEL_ADDRESS.  If NKPML4E
+ * is 1, these are the same, otherwise KPML4BASE < KPML4I and extra
+ * level 4 PDEs are needed to map from VM_MIN_KERNEL_ADDRESS up to
+ * KERNBASE.
+ *
+ * (KPML4I combines with KPDPI to choose where KERNBASE starts.
+ * Or, in other words, KPML4I provides bits 39..47 of KERNBASE,
+ * and KPDPI provides bits 30..38.)
  */
 #define	PML4PML4I	(NPML4EPG/2)	/* Index of recursive pml4 mapping */
 
-#define	KPML4I		(NPML4EPG-1)	/* Top 512GB for KVM */
-#define	DMPML4I		rounddown(KPML4I - NDMPML4E, NDMPML4E) /* Below KVM */
+#define	KPML4BASE	(NPML4EPG-NKPML4E) /* KVM at highest addresses */
+#define	DMPML4I		rounddown(KPML4BASE-NDMPML4E, NDMPML4E) /* Below KVM */
 
+#define	KPML4I		(NPML4EPG-1)
 #define	KPDPI		(NPDPEPG-2)	/* kernbase at -2GB */
 
 /*
diff --git a/sys/amd64/include/vmparam.h b/sys/amd64/include/vmparam.h
index 33f62bd..474ea4b 100644
--- a/sys/amd64/include/vmparam.h
+++ b/sys/amd64/include/vmparam.h
@@ -145,18 +145,19 @@
  * 0x0000000000000000 - 0x00007fffffffffff   user map
  * 0x0000800000000000 - 0xffff7fffffffffff   does not exist (hole)
  * 0xffff800000000000 - 0xffff804020100fff   recursive page table (512GB slot)
- * 0xffff804020101000 - 0xfffffdffffffffff   unused
- * 0xfffffe0000000000 - 0xfffffeffffffffff   1TB direct map
- * 0xffffff0000000000 - 0xffffff7fffffffff   unused
- * 0xffffff8000000000 - 0xffffffffffffffff   512GB kernel map
+ * 0xffff804020101000 - 0xfffff7ffffffffff   unused
+ * 0xfffff80000000000 - 0xfffffbffffffffff   4TB direct map
+ * 0xfffffc0000000000 - 0xfffffdffffffffff   unused
+ * 0xfffffe0000000000 - 0xffffffffffffffff   2TB kernel map
  *
  * Within the kernel map:
  *
  * 0xffffffff80000000                        KERNBASE
  */
 
-#define	VM_MAX_KERNEL_ADDRESS	KVADDR(KPML4I, NPDPEPG-1, NPDEPG-1, NPTEPG-1)
-#define	VM_MIN_KERNEL_ADDRESS	KVADDR(KPML4I, NPDPEPG-512, 0, 0)
+#define	VM_MIN_KERNEL_ADDRESS	KVADDR(KPML4BASE, 0, 0, 0)
+#define	VM_MAX_KERNEL_ADDRESS	KVADDR(KPML4BASE + NKPML4E - 1, \
+					NPDPEPG-1, NPDEPG-1, NPTEPG-1)
 
 #define	DMAP_MIN_ADDRESS	KVADDR(DMPML4I, 0, 0, 0)
 #define	DMAP_MAX_ADDRESS	KVADDR(DMPML4I + NDMPML4E, 0, 0, 0)