kernel: split the page allocator and kmalloc

1 files changed, 108 insertions, 0 deletions

diff --git a/src/kernel/pagealloc.c b/src/kernel/pagealloc.c
new file mode 100644
index 0000000..f01c295
--- /dev/null
+++ b/src/kernel/pagealloc.c
@@ -0,0 +1,108 @@
+#include <kernel/arch/generic.h>
+#include <kernel/malloc.h>
+#include <kernel/panic.h>
+#include <kernel/util.h>
+#include <shared/mem.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+extern uint8_t pbitmap[]; /* linker.ld */
+static size_t pbitmap_len; /* in bytes */
+static void *memtop;
+static void *firstfreepage; /* not necessarily actually free */
+
+static size_t
+toindex(void *p)
+{
+	assert((void*)pbitmap <= p);
+	return ((uintptr_t)p - (uintptr_t)pbitmap) / PAGE_SIZE;
+}
+
+static bool
+pbitmap_get(void *p)
+{
+	size_t i = toindex(p);
+	size_t b = i / 8;
+	uint8_t m = 1 << (i&7);
+	assert(b < pbitmap_len); // TODO the bitmap should be a tad longer
+	return (pbitmap[b]&m) != 0;
+}
+
+static bool
+pbitmap_set(void *p, bool v)
+{
+	size_t i = toindex(p);
+	size_t b = i / 8;
+	uint8_t m = 1 << (i&7);
+	assert(b < pbitmap_len);
+	bool prev = (pbitmap[b]&m) != 0;
+	if (v) {
+		pbitmap[b] |= m;
+	} else {
+		pbitmap[b] &= ~m;
+	}
+	return prev;
+}
+
+void
+mem_init(void *p)
+{
+	memtop = p;
+	kprintf("memory   %8x -> %8x\n", &_bss_end, memtop);
+	pbitmap_len = toindex(memtop) / 8;
+	memset(pbitmap, 0, pbitmap_len);
+	mem_reserve(pbitmap, pbitmap_len);
+	firstfreepage = pbitmap;
+}
+
+void
+mem_reserve(void *addr, size_t len)
+{
+	kprintf("reserved %8x -> %8x\n", addr, addr + len);
+
+	void *top = min(addr + len, memtop);
+	addr = (void*)((uintptr_t)addr & ~PAGE_MASK); /* round down to page */
+	for (void *p = max(addr, (void*)pbitmap); p < top; p += PAGE_SIZE) {
+		/* this doesn't allow overlapping reserved regions, but, more
+		 * importantly, it prevents reserving an already allocated page */
+		if (pbitmap_get(p)) {
+			panic_invalid_state();
+		}
+		pbitmap_set(p, true);
+	}
+}
+
+void *
+page_zalloc(size_t pages)
+{
+	void *p = page_alloc(pages);
+	memset(p, 0, pages * PAGE_SIZE);
+	return p;
+}
+
+void *
+page_alloc(size_t pages)
+{
+	assert(pages == 1);
+	for (void *p = firstfreepage; p < memtop; p += PAGE_SIZE) {
+		if (!pbitmap_get(p)) {
+			pbitmap_set(p, true);
+			firstfreepage = p + PAGE_SIZE;
+			return p;
+		}
+	}
+	kprintf("we ran out of memory :(\ngoodbye.\n");
+	panic_unimplemented();
+}
+
+void
+page_free(void *addr, size_t pages)
+{
+	assert((void*)pbitmap <= addr);
+	for (size_t i = 0; i < pages; i++) {
+		if (pbitmap_set(addr + i*PAGE_SIZE, false) == false) {
+			panic_invalid_state();
+		}
+	}
+	firstfreepage = min(firstfreepage, addr);
+}