Map video memory to mapping area (#108)

* Create a dedicated region of kernel virtual memory for permanent
mappings.
* Map text video memory there instead of the current hack of allocating
mapped pages and then remapping those pages.

This is done in preparation for local APIC support: the APIC's
memory-mapped registers will be mapped in this region as well. This will
likely also be useful to map ACPI tables.

include/kernel/domain/services/mman.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2025 Philippe Aubertin.
+ * All rights reserved.
+
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the author nor the names of other contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JINUE_KERNEL_SERVICES_MMAN_H
+#define JINUE_KERNEL_SERVICES_MMAN_H
+
+#include <kernel/machine/types.h>
+#include <stddef.h>
+
+void *map_in_kernel(kern_paddr_t paddr, size_t size, int prot);
+
+#endif

include/kernel/infrastructure/i686/boot_alloc.h

@@ -37,9 +37,9 @@
 
 void boot_alloc_init(boot_alloc_t *boot_alloc, const bootinfo_t *bootinfo);
 
-void boot_reinit_at_16mb(boot_alloc_t *boot_alloc);
+void boot_alloc_reinit_at_16mb(boot_alloc_t *boot_alloc);
 
-void boot_reinit_at_klimit(boot_alloc_t *boot_alloc);
+void boot_alloc_reinit_at_klimit(boot_alloc_t *boot_alloc);
 
 /**
  * Allocate an object on the boot heap.

include/kernel/infrastructure/i686/exports/asm/machine.h

@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2025 Philippe Aubertin.
+ * All rights reserved.
+
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 
+ * 3. Neither the name of the author nor the names of other contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JINUE_KERNEL_INFRASTRUCTURE_I686_EXPORTS_ASM_MACHINE_H
+#define JINUE_KERNEL_INFRASTRUCTURE_I686_EXPORTS_ASM_MACHINE_H
+
+#define MAPPING_AREA_ADDR   0xf8000000
+
+#define MAPPING_AREA_END    0xffe00000
+
+#endif

include/kernel/infrastructure/i686/pmap/pmap.h

@@ -77,8 +77,6 @@ void pmap_destroy_addr_space(addr_space_t *addr_space);
 
 void pmap_switch_addr_space(addr_space_t *addr_space);
 
-void pmap_boot_map(void *addr, uint32_t paddr, int num_entries);
-
 void pmap_map_kernel_page(void *vaddr, kern_paddr_t paddr, int flags);
 
 void pmap_unmap_kernel_page(void *addr);

include/kernel/machine/asm/machine.h

@@ -34,6 +34,10 @@
 
 #include <jinue/shared/asm/machine.h>
 
+#ifdef __i686__
+#include <kernel/infrastructure/i686/exports/asm/machine.h>
+#endif
+
 /** number of bits in a virtual address that represent the offset within a page */
 #define PAGE_BITS   JINUE_PAGE_BITS
 

kernel/Makefile

@@ -98,6 +98,7 @@ sources.kernel.c = \
 	domain/services/exec.c \
 	domain/services/ipc.c \
 	domain/services/logging.c \
+	domain/services/mman.c \
 	domain/services/panic.c \
 	domain/services/scheduler.c \
 	domain/config.c \

kernel/domain/services/mman.c

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2025 Philippe Aubertin.
+ * All rights reserved.
+
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the author nor the names of other contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <kernel/domain/services/mman.h>
+#include <kernel/domain/services/panic.h>
+#include <kernel/machine/asm/machine.h>
+#include <kernel/machine/pmap.h>
+#include <kernel/machine/spinlock.h>
+#include <kernel/utils/utils.h>
+
+static struct {
+    addr_t      addr;
+    spinlock_t  lock;
+} alloc_state = {
+    .addr   = (addr_t)MAPPING_AREA_ADDR,
+    .lock   = SPINLOCK_INITIALIZER
+};
+
+/**
+ * Permanently map memory in the kernel's mapping area
+ * 
+ * Sufficient virtual memory is allocated in the mapping area, which ranges
+ * from MAPPING_AREA_ADDR to MAPPING_AREA_END. This function panics if
+ * sufficient virtual memory cannot be allocated in this range.
+ * 
+ * There are no alignment requirements: this function takes care of aligning
+ * the mapping on page boundaries.
+ * 
+ * @param paddr address to memory map
+ * @param size size of memory to map
+ * @param prot mapping protection flags
+ */
+void *map_in_kernel(kern_paddr_t paddr, size_t size, int prot) {
+    size_t offset = paddr % PAGE_SIZE;
+
+    size += offset;
+
+    spin_lock(&alloc_state.lock);
+
+    if((addr_t)MAPPING_AREA_END - alloc_state.addr < size) {
+        spin_unlock(&alloc_state.lock);
+        panic("No more space to map memory in kernel");
+    }
+
+    addr_t start = alloc_state.addr;
+    alloc_state.addr = ALIGN_END_PTR(start + size, PAGE_SIZE);
+
+    spin_unlock(&alloc_state.lock);
+
+    addr_t map_addr = start;
+    kern_paddr_t map_paddr = paddr - offset;
+
+    while(true) {
+        machine_map_kernel_page(map_addr, map_paddr, prot);
+
+        if(size <= PAGE_SIZE) {
+            break;
+        }
+
+        map_addr += PAGE_SIZE;
+        map_paddr += PAGE_SIZE;
+        size -= PAGE_SIZE;
+    }
+
+    return start + offset;
+}

kernel/infrastructure/i686/boot_alloc.c

@@ -46,7 +46,7 @@
  *
  * This function sets up the allocator to allocate pages after the kernel loaded
  * at 0x100000 (1MB). Once the kernel has been moved to 0x1000000 (16MB), the
- * boot_reinit_at_16mb() function has to be called to start allocating pages
+ * boot_alloc_reinit_at_16mb() function has to be called to start allocating pages
  * there.
  *
  * @param boot_alloc the allocator state initialized by this function
@@ -71,7 +71,7 @@ void boot_alloc_init(boot_alloc_t *boot_alloc, const bootinfo_t *bootinfo) {
  * @param boot_alloc the allocator state initialized by this function
  *
  * */
-void boot_reinit_at_16mb(boot_alloc_t *boot_alloc) {
+void boot_alloc_reinit_at_16mb(boot_alloc_t *boot_alloc) {
     boot_alloc->current_page        = boot_alloc->first_page_at_16mb;
     boot_alloc->page_limit          = (char *)MEMORY_ADDR_16MB + BOOT_SIZE_AT_16MB;
 }
@@ -90,7 +90,7 @@ void boot_reinit_at_16mb(boot_alloc_t *boot_alloc) {
  * @param boot_alloc the allocator state initialized by this function
  *
  * */
-void boot_reinit_at_klimit(boot_alloc_t *boot_alloc) {
+void boot_alloc_reinit_at_klimit(boot_alloc_t *boot_alloc) {
     boot_alloc->current_page        = (void *)PHYS_TO_VIRT_AT_16MB(boot_alloc->current_page);
     boot_alloc->page_limit          = (char *)KLIMIT + BOOT_SIZE_AT_16MB;
 }

kernel/infrastructure/i686/init.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2019-2024 Philippe Aubertin.
+ * Copyright (C) 2019-2025 Philippe Aubertin.
  * All rights reserved.
 
  * Redistribution and use in source and binary forms, with or without
@@ -29,10 +29,12 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <jinue/shared/asm/mman.h>
 #include <jinue/shared/asm/syscalls.h>
 #include <kernel/domain/alloc/page_alloc.h>
 #include <kernel/domain/services/cmdline.h>
 #include <kernel/domain/services/logging.h>
+#include <kernel/domain/services/mman.h>
 #include <kernel/domain/services/panic.h>
 #include <kernel/infrastructure/i686/asm/msr.h>
 #include <kernel/infrastructure/i686/drivers/acpi.h>
@@ -199,30 +201,24 @@ static void load_selectors(percpu_t *cpu_data, boot_alloc_t *boot_alloc) {
     boot_heap_pop(boot_alloc);
 }
 
-static void remap_text_video_memory(boot_alloc_t *boot_alloc) {
-    size_t video_buffer_size    = VGA_TEXT_VID_TOP - VGA_TEXT_VID_BASE;
-    size_t num_pages            = video_buffer_size / PAGE_SIZE;
-
-    void *buffer = boot_page_alloc_n(boot_alloc, num_pages);
-    void *mapped = (void *)PHYS_TO_VIRT_AT_16MB(buffer);
-
-    pmap_boot_map(mapped, VGA_TEXT_VID_BASE, num_pages);
-
-    info("Remapping text video memory at %#p", mapped);
-
-    /* Note: after this call to vga_set_base_addr() until we switch to the new
-     * new address space, VGA output is not possible. Attempting it will cause
-     * a kernel panic due to a page fault (and the panic handler itself attempts
-     * to log). */
-    vga_set_base_addr(mapped);
-}
-
 static void enable_global_pages(void) {
     if(cpu_has_feature(CPUINFO_FEATURE_PGE)) {
         set_cr4(get_cr4() | X86_CR4_PGE);
     }
 }
 
+static void remap_text_video_memory(void) {
+    void *mapped = map_in_kernel(
+        VGA_TEXT_VID_BASE,
+        VGA_TEXT_VID_TOP - VGA_TEXT_VID_BASE,
+        JINUE_PROT_READ | JINUE_PROT_WRITE
+    );
+
+    vga_set_base_addr(mapped);
+
+    info("Remapped text video memory at %#p", mapped);    
+}
+
 static void initialize_page_allocator(boot_alloc_t *boot_alloc) {
     while(! boot_page_alloc_is_empty(boot_alloc)) {
         page_free(boot_page_alloc(boot_alloc));
@@ -346,7 +342,7 @@ void machine_init(const config_t *config) {
      * Do this after enabling PAE: we want the temporary PAE page tables to be
      * allocated after 1MB because we won't need them anymore once the final
      * address space is created. */
-    boot_reinit_at_16mb(&boot_alloc);
+    boot_alloc_reinit_at_16mb(&boot_alloc);
 
     /* allocate per-CPU data
      * 
@@ -383,21 +379,19 @@ void machine_init(const config_t *config) {
 
     memory_initialize_array(&boot_alloc, bootinfo);
 
-    /* After this, VGA output is not possible until we switch to the
-     * new address space (see the call to pmap_switch_addr_space() below).
-     * Attempting it will cause a kernel panic due to a page fault (and the
-     * panic handler itself attempts to log). */
-    remap_text_video_memory(&boot_alloc);
-
     /* switch to new address space */
     pmap_switch_addr_space(addr_space);
 
     enable_global_pages();
-
-    /* From this point, we are ready to switch to the new address space, so we
-     * don't need to allocate any more pages from the boot allocator. Transfer
-     * the remaining pages to the run-time page allocator. */
-    boot_reinit_at_klimit(&boot_alloc);
+
+    /* This should be done early after calling pmap_switch_addr_space()
+     * because, until it's done, any attempt to log anything to VGA will
+     * result in a kernel panic caused by a kernel page fault (and the
+     * panic handler itself will then attempt to log). */
+    remap_text_video_memory();
+
+    /* Transfer the remaining pages to the run-time page allocator. */
+    boot_alloc_reinit_at_klimit(&boot_alloc);
     initialize_page_allocator(&boot_alloc);
 
     /* create slab cache to allocate PDPTs

kernel/infrastructure/i686/pmap/pmap.c

@@ -535,18 +535,6 @@ void pmap_switch_addr_space(addr_space_t *addr_space) {
     cpu_data->current_addr_space = addr_space;
 }
 
-void pmap_boot_map(void *addr, uint32_t paddr, int num_entries) {
-    int offset = (uintptr_t)((char *)addr - KLIMIT) / PAGE_SIZE;
-
-    initialize_page_table_linear(
-            get_pte_with_offset(
-                    (pte_t *)PTR_TO_PHYS_ADDR_AT_16MB(kernel_page_tables),
-                    offset),
-            paddr,
-            X86_PTE_READ_WRITE,
-            num_entries);
-}
-
 static pte_t *pmap_lookup_page_table(
         addr_space_t    *addr_space,
         void            *addr,