pmm: properly detect first available memory region

For the first available usable region we need a space of at least
EARLY_VIRT_MEM MB, which is not below first MB.
Since some UEFI firmware allocates more than one usable region
below the first MB with size of 4096 bytes, it is better to
dynamically scan all usable regions and select the first one
matching above criteria.

Signed-off-by: Pawel Wieczorkiewicz <[email protected]>

mm/pmm.c

@@ -30,8 +30,6 @@
 #include <mm/regions.h>
 #include <mm/vmm.h>
 
-#define PMM_FIRST_AVAIL_REGION 1
-
 size_t total_phys_memory;
 
 static list_head_t frames;
@@ -246,7 +244,27 @@ static inline unsigned int find_max_avail_order(size_t size) {
     return PAGE_ORDER_4K;
 }
 
-static size_t process_memory_range(unsigned index) {
+static unsigned find_first_avail_region(void) {
+    addr_range_t range;
+
+    for (unsigned int i = 0; i < regions_num; i++) {
+        if (get_avail_memory_range(i, &range) < 0)
+            continue;
+
+        if (_paddr(range.start) < _paddr(MB(1)))
+            continue;
+
+        if (_paddr(range.end) - _paddr(range.start) < MB(EARLY_VIRT_MEM))
+            continue;
+
+        return i;
+    }
+
+    panic("PMM: Cannot obtain first available physical memory address range\n");
+    UNREACHABLE();
+}
+
+static size_t process_memory_range(unsigned index, unsigned first_avail_region) {
     paddr_t start, end, cur;
     unsigned int max_order;
     addr_range_t range;
@@ -267,7 +285,7 @@ static size_t process_memory_range(unsigned index) {
 
     /* Add initial 4K frames and align to 2M. */
     while ((cur < MB(EARLY_VIRT_MEM) || cur % PAGE_SIZE_2M) && cur + PAGE_SIZE <= end) {
-        if (index <= PMM_FIRST_AVAIL_REGION)
+        if (index <= first_avail_region)
             add_early_frame(paddr_to_mfn(cur), PAGE_ORDER_4K);
         else
             add_frame(paddr_to_mfn(cur), PAGE_ORDER_4K);
@@ -320,11 +338,11 @@ void reclaim_frame(mfn_t mfn, unsigned int order) {
     add_frame(mfn, order);
 }
 
-static inline void check_early_frames(void) {
+static inline void check_early_frames(unsigned first_avail_region) {
     unsigned early_frames_cnt;
     addr_range_t range;
 
-    if (get_avail_memory_range(PMM_FIRST_AVAIL_REGION, &range) < 0)
+    if (get_avail_memory_range(first_avail_region, &range) < 0)
         panic("PMM: Cannot obtain first available physical memory address range\n");
 
     early_frames_cnt =
@@ -336,6 +354,8 @@ static inline void check_early_frames(void) {
 }
 
 void init_pmm(void) {
+    unsigned first_region_index;
+
     printk("Initialize Physical Memory Manager\n");
 
     BUILD_BUG_ON(sizeof(frames_array_t) > PAGE_SIZE);
@@ -348,13 +368,15 @@ void init_pmm(void) {
         list_init(&busy_frames[order]);
     }
 
+    first_region_index = find_first_avail_region();
+
     /* Skip low memory range */
-    for (unsigned int i = PMM_FIRST_AVAIL_REGION; i < regions_num; i++)
-        total_phys_memory += process_memory_range(i);
+    for (unsigned int i = first_region_index; i < regions_num; i++)
+        total_phys_memory += process_memory_range(i, first_region_index);
 
     display_frames_count();
 
-    check_early_frames();
+    check_early_frames(first_region_index);
 
     if (opt_debug)
         display_frames();