setup, multiboot: add map_multiboot_areas() function

The multiboot provided memory is referenced after initial boot phase
for information about available physical memory, kernel command line,
etc.

Add map_multiboot_areas() that explicitely maps multiboot areas into
final page tables.

This is needed to get rid of "Low memory" static mapping.

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

Author: wipawel

arch/x86/boot/multiboot.c

@@ -81,6 +81,33 @@ void init_multiboot(multiboot_info_t *mbi, const char **cmdline) {
         *cmdline = (const char *) _ptr(mbi->cmdline);
 }
 
+void map_multiboot_areas(void) {
+    paddr_t mbi = _paddr(multiboot_info);
+
+    vmap_4k(paddr_to_virt(mbi), paddr_to_mfn(mbi), L1_PROT_RO);
+    kmap_4k(paddr_to_mfn(mbi), L1_PROT_RO);
+
+    if (has_mbi_flag(MULTIBOOT_INFO_MEM_MAP)) {
+        paddr_t mmap_start = _paddr(multiboot_info->mmap_addr);
+        paddr_t mmap_stop = mmap_start + _paddr(multiboot_info->mmap_length);
+
+        for (mfn_t mmap_mfn = paddr_to_mfn(mmap_start);
+             mmap_mfn < paddr_to_mfn(mmap_stop); mmap_mfn++) {
+            vmap_4k(mfn_to_virt(mmap_mfn), mmap_mfn, L1_PROT_RO);
+            kmap_4k(mmap_mfn, L1_PROT_RO);
+        }
+    }
+
+    if (has_mbi_flag(MULTIBOOT_INFO_CMDLINE)) {
+        paddr_t cmdline_start = _paddr(multiboot_info->cmdline);
+        paddr_t cmdline_stop = cmdline_start + strlen((const char *) _ptr(cmdline_start));
+
+        for (mfn_t cmdline_mfn = paddr_to_mfn(cmdline_start);
+             cmdline_mfn < paddr_to_mfn(cmdline_stop); cmdline_mfn++)
+            kmap_4k(cmdline_mfn, L1_PROT_RO);
+    }
+}
+
 unsigned mbi_get_avail_memory_ranges_num(void) {
     unsigned num = 0;
 

common/setup.c

@@ -218,6 +218,9 @@ void __noreturn __text_init kernel_start(uint32_t multiboot_magic,
 
     /* Setup final pagetables */
     init_pagetables();
+
+    map_multiboot_areas();
+
     write_cr3(cr3.paddr);
     WRITE_SP(get_free_pages_top(PAGE_ORDER_2M, GFP_KERNEL));
     if (opt_debug)

include/multiboot.h

@@ -292,6 +292,7 @@ extern void init_multiboot(multiboot_info_t *mbi, const char **cmdline);
 
 #include <mm/pmm.h>
 #include <page.h>
+extern void map_multiboot_areas(void);
 extern unsigned mbi_get_avail_memory_ranges_num(void);
 extern int mbi_get_avail_memory_range(unsigned index, addr_range_t *r);
 extern int mbi_get_memory_range(paddr_t pa, addr_range_t *r);