amd64: allow base memory segment to start at address different than 0

Current code requires that the first physical memory segment starts at 0,
but this is not really needed. We only need to make sure the bootstrap code
and page tables for APs are allocated below 4GB.

This patch removes this requirement and allows booting a Dell R710 from
UEFI, where the first physical memory segment starts at 0x10000.

Sponsored by: Citrix Systems R&D
Reviewed by: jhb
Differential Revision: https://reviews.freebsd.org/D1417

1 files changed, 25 insertions, 13 deletions

diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 07378fdd..839da01 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -1355,8 +1355,10 @@ add_physmap_entry(uint64_t base, uint64_t length, vm_paddr_t *physmap,
 	/*
 	 * Find insertion point while checking for overlap.  Start off by
 	 * assuming the new entry will be added to the end.
+	 *
+	 * NB: physmap_idx points to the next free slot.
 	 */
-	insert_idx = physmap_idx + 2;
+	insert_idx = physmap_idx;
 	for (i = 0; i <= physmap_idx; i += 2) {
 		if (base < physmap[i + 1]) {
 			if (base + length <= physmap[i]) {
@@ -1394,7 +1396,7 @@ add_physmap_entry(uint64_t base, uint64_t length, vm_paddr_t *physmap,
 	 * Move the last 'N' entries down to make room for the new
 	 * entry if needed.
 	 */
-	for (i = physmap_idx; i > insert_idx; i -= 2) {
+	for (i = (physmap_idx - 2); i > insert_idx; i -= 2) {
 		physmap[i] = physmap[i - 2];
 		physmap[i + 1] = physmap[i - 1];
 	}
@@ -1580,23 +1582,27 @@ getmemsize(caddr_t kmdp, u_int64_t first)
 	int page_counter;
 
 	bzero(physmap, sizeof(physmap));
-	basemem = 0;
 	physmap_idx = 0;
 
 	init_ops.parse_memmap(kmdp, physmap, &physmap_idx);
+	physmap_idx -= 2;
 
 	/*
 	 * Find the 'base memory' segment for SMP
 	 */
 	basemem = 0;
 	for (i = 0; i <= physmap_idx; i += 2) {
-		if (physmap[i] == 0x00000000) {
+		if (physmap[i] <= 0xA0000) {
 			basemem = physmap[i + 1] / 1024;
 			break;
 		}
 	}
-	if (basemem == 0)
-		panic("BIOS smap did not include a basemem segment!");
+	if (basemem == 0 || basemem > 640) {
+		if (bootverbose)
+			printf(
+		"Memory map doesn't contain a basemem segment, faking it");
+		basemem = 640;
+	}
 
 	/*
 	 * Make hole for "AP -> long mode" bootstrap code.  The
@@ -1604,8 +1610,12 @@ getmemsize(caddr_t kmdp, u_int64_t first)
 	 * is configured to support APs and APs for the system start
 	 * in 32bit mode (e.g. SMP bare metal).
 	 */
-	if (init_ops.mp_bootaddress)
+	if (init_ops.mp_bootaddress) {
+		if (physmap[1] >= 0x100000000)
+			panic(
+	"Basemem segment is not suitable for AP bootstrap code!");
 		physmap[1] = init_ops.mp_bootaddress(physmap[1] / 1024);
+	}
 
 	/*
 	 * Maxmem isn't the "maximum memory", it's one larger than the
@@ -1657,12 +1667,14 @@ getmemsize(caddr_t kmdp, u_int64_t first)
 	 */
 	physmem_start = (vm_guest > VM_GUEST_NO ? 1 : 16) << PAGE_SHIFT;
 	TUNABLE_ULONG_FETCH("hw.physmem.start", &physmem_start);
-	if (physmem_start < PAGE_SIZE)
-		physmap[0] = PAGE_SIZE;
-	else if (physmem_start >= physmap[1])
-		physmap[0] = round_page(physmap[1] - PAGE_SIZE);
-	else
-		physmap[0] = round_page(physmem_start);
+	if (physmap[0] < physmem_start) {
+		if (physmem_start < PAGE_SIZE)
+			physmap[0] = PAGE_SIZE;
+		else if (physmem_start >= physmap[1])
+			physmap[0] = round_page(physmap[1] - PAGE_SIZE);
+		else
+			physmap[0] = round_page(physmem_start);
+	}
 	pa_indx = 0;
 	da_indx = 1;
 	phys_avail[pa_indx++] = physmap[0];