From c51e1d7c0a79a4fe2774d526ad0393cd2edd3f6c Mon Sep 17 00:00:00 2001
From: Warner Losh <imp@FreeBSD.org>
Date: Fri, 2 Dec 2022 11:10:42 -0700
Subject: [PATCH] kboot: amd64 use /sys/firmware/memmap to find free memory

Use the system's firmware memory map to find a good place to put the
kernel that won't stomp on anything else. While this uses obstensibly MI
interfaces to get this data, arm64 doesn't have this, nor does
powerpc64, so place it here.

Sponsored by:		Netflix
---
 stand/kboot/arch/amd64/load_addr.c | 127 ++++++++++++++++++++++++++++-
 1 file changed, 126 insertions(+), 1 deletion(-)

diff --git a/stand/kboot/arch/amd64/load_addr.c b/stand/kboot/arch/amd64/load_addr.c
index cbe066d02d40..fccd17cf8d51 100644
--- a/stand/kboot/arch/amd64/load_addr.c
+++ b/stand/kboot/arch/amd64/load_addr.c
@@ -30,8 +30,133 @@
 #include "host_syscall.h"
 #include "kboot.h"
 
+/* Refactor when we do arm64 */
+
+struct memory_segments
+{
+	uint64_t	start;
+	uint64_t	end;
+	uint64_t	type;
+};
+
+enum types {
+	system_ram = 1,
+	acpi_tables,
+	acpi_nv_storage,
+	unusable,
+	persistent_old,
+	persistent,
+	soft_reserved,
+	reserved,
+};
+
+struct kv
+{
+	uint64_t	type;
+	char *		name;
+} str2type_kv[] = {
+	{ system_ram,		"System RAM" },
+	{ acpi_tables,		"ACPI Tables" },
+	{ acpi_nv_storage,	"ACPI Non-volatile Storage" },
+	{ unusable,		"Unusable memory" },
+	{ persistent_old,	"Persistent Memory (legacy)" },
+	{ persistent,		"Persistent Memory" },
+	{ soft_reserved,	"Soft Reserved" },
+	{ reserved,		"reserved" },
+	{ 0, NULL },
+};
+
+#define MEMMAP "/sys/firmware/memmap"
+
+static bool
+str2type(struct kv *kv, const char *buf, uint64_t *value)
+{
+	while (kv->name != NULL) {
+		if (strcmp(kv->name, buf) == 0) {
+			*value = kv->type;
+			return true;
+		}
+		kv++;
+	}
+
+	return false;
+}
+
+static int
+read_memmap(struct memory_segments *segs, int maxseg)
+{
+	int n;
+	char name[MAXPATHLEN];
+	char buf[80];
+
+	n = 0;
+	do {
+		snprintf(name, sizeof(name), "%s/%d/start", MEMMAP, n);
+		if (!file2u64(name, &segs[n].start))
+			break;
+		snprintf(name, sizeof(name), "%s/%d/length", MEMMAP, n);
+		if (!file2u64(name, &segs[n].end))
+			break;
+		snprintf(name, sizeof(name), "%s/%d/type", MEMMAP, n);
+		if (!file2str(name, buf, sizeof(buf)))
+			break;
+		if (!str2type(str2type_kv, buf, &segs[n].type))
+			break;
+		n++;
+	} while (n < maxseg);
+
+	return n;
+}
+
+#define BAD_SEG ~0ULL
+
+#define SZ(s) (((s).end - (s).start) + 1)
+
+static uint64_t
+find_ram(struct memory_segments *segs, int nr_seg, uint64_t minpa, uint64_t align,
+    uint64_t sz, uint64_t maxpa)
+{
+	uint64_t start;
+
+	/* XXX assume segs are sorted in numeric order -- assumed not ensured */
+	for (int i = 0; i < nr_seg; i++) {
+		if (segs[i].type != system_ram ||
+		    SZ(segs[i]) < sz ||
+		    minpa + sz > segs[i].end ||
+		    maxpa < segs[i].start)
+			continue;
+		start = roundup(segs[i].start, align);
+		if (start < minpa)	/* Too small, round up and try again */
+			start = (roundup(minpa, align));
+		if (start + sz > segs[i].end)	/* doesn't fit in seg */
+			continue;
+		if (start > maxpa ||		/* Over the edge */
+		    start + sz > maxpa)		/* on the edge */
+			break;			/* No hope to continue */
+		return start;
+	}
+
+	return BAD_SEG;
+}
+
 uint64_t
 kboot_get_phys_load_segment(void)
 {
-	return (~0ULL);
+	static uint64_t base_seg = BAD_SEG;
+	struct memory_segments segs[32];
+	int nr_seg;
+
+	if (base_seg != BAD_SEG)
+		return (base_seg);
+
+	nr_seg = read_memmap(segs, nitems(segs));
+	if (nr_seg > 0)
+		base_seg = find_ram(segs, nr_seg, 2ULL << 20, 2ULL << 20,
+		    64ULL << 20, 4ULL << 30);
+	if (base_seg == BAD_SEG) {
+		/* XXX Should fall back to using /proc/iomem maybe? */
+		/* XXX PUNT UNTIL I NEED SOMETHING BETTER */
+		base_seg = 42ULL * (1 << 20); /* Jam it in at the odd-ball address of 42MB so it stands out */
+	}
+	return (base_seg);
 }