start working on virtual memory

1 files changed, 137 insertions, 10 deletions

diff --git a/triscv/src/mmu.c b/triscv/src/mmu.c
index c73f91d..c90c51d 100644
--- a/triscv/src/mmu.c
+++ b/triscv/src/mmu.c
@@ -1,9 +1,11 @@
 #include <triscv/mmu.h>
+#include <triscv/csr.h>
 
+/* from and to must be page aligned, each tlb in map represent a base page. */
 struct tlb_map {
 	vm_t from;
 	pm_t to;
-	bool valid;
+	tri_t tag;
 };
 
 struct dev_map {
@@ -45,7 +47,7 @@ static struct dev_map *mmu_find_dev_map(struct mmu *mmu, pm_t addr)
 			continue;
 
 		/* slightly tricky off by one here */
-		if (d->dev.size <= (addr - d->start))
+		if (d->start + (pm_t)d->dev.size <= addr)
 			continue;
 
 		return d;
@@ -69,6 +71,25 @@ stat_t mmu_map_dev(struct mmu *mmu, pm_t start, struct dev dev)
 	return OK;
 }
 
+struct tri_option {
+	tri_t value;
+	bool ok;
+};
+
+static struct tri_option __mmu_read3(struct cpu *cpu, struct mmu *mmu, vm_t addr)
+{
+	struct dev_map *d = mmu_find_dev_map(mmu, addr);
+	if (!d || !d->dev.read3) {
+		/** @todo raise bus error */
+		return (struct tri_option){.ok = false};
+	}
+
+	return (struct tri_option){
+		.value = d->dev.read3(cpu, d->dev.dev, addr - d->start),
+		.ok = true
+	};
+}
+
 void mmu_enable(struct mmu *mmu)
 {
 	mmu->translate = true;
@@ -79,12 +100,114 @@ void mmu_disable(struct mmu *mmu)
 	mmu->translate = false;
 }
 
+static bool __valid_mapping(struct tlb_map mapping)
+{
+	return !(mapping.from == 1 && mapping.to == 1);
+}
+
+static struct tlb_map __build_invalid_mapping()
+{
+	return (struct tlb_map){.from = 1, .to = 1};
+}
+
+static struct tlb_map __build_mapping(vm_t from, pm_t to, tri_t tag)
+{
+	return (struct tlb_map){.from = from, .to = to, .tag = tag};
+}
+
+static bool __valid_pte(tri_t pte)
+{
+	return tri_get_trit(pte, 0) == 1;
+}
+
+static bool __leaf_pte(tri_t pte)
+{
+	int rw = tri_get_trit(pte, 1);
+	int x = tri_get_trit(pte, 3);
+
+	return !(x == 0 && rw == 0);
+}
+
+static pm_t __process_pte(struct cpu *cpu, struct mmu *mmu, pm_t table, tri_t orig, size_t shift,
+		struct tlb_map *mapping)
+{
+	tri_t ppn = tri_mask(tri_sr(orig, shift), 6);
+	pm_t i = tri_to(ppn);
+	struct tri_option pte = __mmu_read3(cpu, mmu, table + 3 * i);
+
+	if (!pte.ok || !__valid_pte(pte.value)) {
+		*mapping = __build_invalid_mapping();
+		return 0;
+	}
+
+	if (__leaf_pte(pte.value)) {
+		// pte was fine, so the tag must be as well
+		tri_t tag = __mmu_read3(cpu, mmu, table + 3 * i + 3).value;
+
+		tri_t base = tri_discard(pte.value, 9);
+		tri_t cur = tri_discard(orig, shift);
+		tri_t off = tri_sub(orig, cur);
+
+		*mapping = __build_mapping(tri_to(orig), tri_to(base) + tri_to(off), tag);
+		return 0;
+	}
+
+	return pte.value;
+}
+
+static struct tlb_map __fetch_mapping(struct cpu *cpu, struct mmu *mmu, vm_t addr)
+{
+	/* feels kind of silly to convert back to trinary, but I guess fine for
+	 * now. */
+	tri_t orig = tri_from(addr);
+
+	int sign = tri_sign(orig);
+
+	tri_t start = 0;
+	switch (sign) {
+	case  1: start = get_csr(cpu, CSR_SATPP); break;
+	case  0: start = get_csr(cpu, CSR_SATPO); break;
+	case -1: start = get_csr(cpu, CSR_SATPN); break;
+	}
+
+	start = tri_to(start);
+
+	tri_t pte = 0;
+	struct tlb_map mapping = {0};
+	if (!(pte = __process_pte(cpu, mmu, start, orig, 21, &mapping)))
+		return mapping;
+
+	start = tri_to(tri_discard(pte, 9));
+	if (!(pte = __process_pte(cpu, mmu, start, orig, 15, &mapping)))
+		return mapping;
+
+	start = tri_to(tri_discard(pte, 9));
+	if (!(pte = __process_pte(cpu, mmu, start, orig, 9, &mapping)))
+		return mapping;
+
+	return __build_invalid_mapping();
+}
+
 static bool mmu_translate(struct cpu *cpu, struct mmu *mmu, vm_t *addr)
 {
 	(void)cpu;
-	(void)mmu;
-	(void)addr;
-	/** @todo raise segfault if addr is not allowed */
+
+	vm_t base_page = *addr / BASE_PAGE_SIZE;
+	vm_t base_addr = base_page * BASE_PAGE_SIZE;
+	size_t slot = (size_t)base_page % MMU_SIZE;
+	vm_t offset = *addr - base_addr;
+
+	struct tlb_map mapping = mmu->tlb[slot];
+	if (mapping.from != base_addr || !__valid_mapping(mapping))
+		mmu->tlb[slot] = mapping = __fetch_mapping(cpu, mmu, base_addr);
+
+	if (mapping.from != base_addr || !__valid_mapping(mapping)) {
+		/* @todo raise segfault */
+		return false;
+	}
+
+	/* @todo check rwx and tags */
+	*addr = mapping.to + offset;
 	return true;
 }
 
@@ -141,11 +264,15 @@ tri_t mmu_read3(struct cpu *cpu, struct mmu *mmu, vm_t addr)
 			return 0;
 	}
 
-	struct dev_map *d = mmu_find_dev_map(mmu, addr);
-	if (!d || !d->dev.read3) {
-		/** @todo raise bus error */
-		return 0;
+	return __mmu_read3(cpu, mmu, addr).value;
+}
+
+tri_t mmu_read_pc(struct cpu *cpu, struct mmu *mmu, vm_t addr)
+{
+	if (mmu->translate) {
+		if (!mmu_translate(cpu, mmu, &addr))
+			return 0;
 	}
 
-	return d->dev.read3(cpu, d->dev.dev, addr - d->start);
+	return __mmu_read3(cpu, mmu, addr).value;
 }