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[platform][pc] use legacy memory descriptor if multiboot doesn't pass…
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… new style

Use the legacy version of the memory sizing info that just hands the
kernel 2 implicit ranges: 0 ... X and 1MB ... Y.

Not ideal, but when booting on very old machines without BIOS e820 call
implemented it's all you got.
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@travisg
travisg committed Mar 8, 2024
1 parent ed2a3a7 commit ed309d2
Showing 1 changed file with 76 additions and 55 deletions.
131 changes: 76 additions & 55 deletions platform/pc/platform.c
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Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,66 @@ extern uint64_t __bss_end;
#define NUM_ARENAS 16
static pmm_arena_t mem_arena[NUM_ARENAS];

/* parse an array of multiboot mmap entries */
static status_t parse_multiboot_mmap(const memory_map_t *mmap, const size_t mmap_length, size_t *found_mem_arenas) {
for (uint i = 0; i < mmap_length / sizeof(memory_map_t); i++) {

uint64_t base = mmap[i].base_addr_low | (uint64_t)mmap[i].base_addr_high << 32;
uint64_t length = mmap[i].length_low | (uint64_t)mmap[i].length_high << 32;

dprintf(SPEW, "\ttype %u addr %#" PRIx64 " len %#" PRIx64 "\n",
mmap[i].type, base, length);
if (mmap[i].type == MB_MMAP_TYPE_AVAILABLE) {

/* do some sanity checks to cut out small arenas */
if (length < PAGE_SIZE * 2) {
continue;
}

/* align the base and length */
uint64_t oldbase = base;
base = PAGE_ALIGN(base);
if (base > oldbase) {
length -= base - oldbase;
}
length = ROUNDDOWN(length, PAGE_SIZE);

/* ignore memory < 1MB */
if (base < 1*MB) {
/* skip everything < 1MB */
continue;
}

/* ignore everything that extends past the size PHYSMAP maps into the kernel.
* see arch/x86/arch.c mmu_initial_mappings
*/
if (base >= PHYSMAP_SIZE) {
continue;
}
uint64_t end = base + length;
if (end > PHYSMAP_SIZE) {
end = PHYSMAP_SIZE;
DEBUG_ASSERT(end > base);
length = end - base;
dprintf(INFO, "PC: trimmed memory to %" PRIu64 " bytes\n", PHYSMAP_SIZE);
}

/* initialize a new pmm arena */
mem_arena[*found_mem_arenas].name = "memory";
mem_arena[*found_mem_arenas].base = base;
mem_arena[*found_mem_arenas].size = length;
mem_arena[*found_mem_arenas].priority = 1;
mem_arena[*found_mem_arenas].flags = PMM_ARENA_FLAG_KMAP;
(*found_mem_arenas)++;
if (*found_mem_arenas == countof(mem_arena)) {
break;
}
}
}

return NO_ERROR;
}

/* Walk through the multiboot structure and attempt to discover all of the runs
* of physical memory to bootstrap the pmm areas.
* Returns number of arenas initialized in passed in pointer
Expand All @@ -73,70 +133,31 @@ static status_t platform_parse_multiboot_info(size_t *found_mem_arenas) {

dprintf(SPEW, "\tflags %#x\n", multiboot_info->flags);

// legacy multiboot memory size field
if (multiboot_info->flags & MB_INFO_MEM_SIZE) {
dprintf(SPEW, "PC: multiboot memory lower %#x upper %#" PRIx64 "\n",
multiboot_info->mem_lower * 1024U, multiboot_info->mem_upper * 1024ULL);
if ((multiboot_info->flags & MB_INFO_MMAP) == 0) {
// There is no mmap to give us a more detailed memory map
// so we'll need to use this one. Synthesize a fake mmap array to pass
// to the mmap code.
memory_map_t mmap[2] = {};
mmap[0].length_low = multiboot_info->mem_lower * 1024U;
mmap[0].type = MB_MMAP_TYPE_AVAILABLE;
mmap[1].base_addr_low = 1 * 1024U * 1024U;
mmap[1].length_low = multiboot_info->mem_upper * 1024U;
mmap[1].type = MB_MMAP_TYPE_AVAILABLE;
parse_multiboot_mmap(mmap, 2 * sizeof(memory_map_t), found_mem_arenas);
}
}

// more modern multiboot mmap array
if (multiboot_info->flags & MB_INFO_MMAP) {
const memory_map_t *mmap = (const memory_map_t *)(uintptr_t)multiboot_info->mmap_addr;
mmap = (void *)((uintptr_t)mmap + KERNEL_BASE);

dprintf(SPEW, "PC: multiboot memory map, length %u:\n", multiboot_info->mmap_length);
for (uint i = 0; i < multiboot_info->mmap_length / sizeof(memory_map_t); i++) {

uint64_t base = mmap[i].base_addr_low | (uint64_t)mmap[i].base_addr_high << 32;
uint64_t length = mmap[i].length_low | (uint64_t)mmap[i].length_high << 32;

dprintf(SPEW, "\ttype %u addr %#" PRIx64 " len %#" PRIx64 "\n",
mmap[i].type, base, length);
if (mmap[i].type == MB_MMAP_TYPE_AVAILABLE) {

/* do some sanity checks to cut out small arenas */
if (length < PAGE_SIZE * 2) {
continue;
}

/* align the base and length */
uint64_t oldbase = base;
base = PAGE_ALIGN(base);
if (base > oldbase) {
length -= base - oldbase;
}
length = ROUNDDOWN(length, PAGE_SIZE);

/* ignore memory < 1MB */
if (base < 1*MB) {
/* skip everything < 1MB */
continue;
}

/* ignore everything that extends past the size PHYSMAP maps into the kernel.
* see arch/x86/arch.c mmu_initial_mappings
*/
if (base >= PHYSMAP_SIZE) {
continue;
}
uint64_t end = base + length;
if (end > PHYSMAP_SIZE) {
end = PHYSMAP_SIZE;
DEBUG_ASSERT(end > base);
length = end - base;
dprintf(INFO, "PC: trimmed memory to %" PRIu64 " bytes\n", PHYSMAP_SIZE);
}

/* initialize a new pmm arena */
mem_arena[*found_mem_arenas].name = "memory";
mem_arena[*found_mem_arenas].base = base;
mem_arena[*found_mem_arenas].size = length;
mem_arena[*found_mem_arenas].priority = 1;
mem_arena[*found_mem_arenas].flags = PMM_ARENA_FLAG_KMAP;
(*found_mem_arenas)++;
if (*found_mem_arenas == countof(mem_arena)) {
break;
}
}
}
parse_multiboot_mmap(mmap, multiboot_info->mmap_length, found_mem_arenas);
}

if (multiboot_info->flags & MB_INFO_FRAMEBUFFER) {
Expand Down Expand Up @@ -175,7 +196,7 @@ void platform_early_init(void) {
platform_parse_multiboot_info(&found_arenas);
if (found_arenas <= 0) {
/* if we couldn't find any memory, initialize a default arena */
mem_arena[0] = (pmm_arena_t){
mem_arena[0] = (pmm_arena_t) {
.name = "memory",
.base = MEMBASE,
.size = DEFAULT_MEMEND,
Expand Down

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