From 0b6a1d1d0e76ba9b77b6709aff1551df5ca1cb3a Mon Sep 17 00:00:00 2001
From: Augustin Cavalier <waddlesplash@gmail.com>
Date: Wed, 16 Oct 2024 15:42:21 -0400
Subject: [PATCH] bootloader/bios_ia32: Restore split between kernel and identity map allocation.

This mostly reverts commit 19141f2110472c0b9b5227e5411f7e1b9f98fe8b,
thus restoring most of the changes from 8b813adf6df7c4ec2c988888a5b6ef2e398aa103.

However, we keep these ranges inside the kernel args ranges for now,
as they're used in the 32-bit non-PAE case at least.
---

diff --git a/src/system/boot/platform/bios_ia32/mmu.cpp b/src/system/boot/platform/bios_ia32/mmu.cpp
index 3ba6547..4894d1b 100644
--- a/src/system/boot/platform/bios_ia32/mmu.cpp
+++ b/src/system/boot/platform/bios_ia32/mmu.cpp
@@ -81,6 +81,7 @@
 #ifdef _PXE_ENV
 
 static addr_t sNextPhysicalAddress = 0x112000;
+static addr_t sNextPhysicalKernelAddress = kIdentityMapEnd;
 static addr_t sNextVirtualAddress = KERNEL_LOAD_BASE + kMaxKernelSize;
 
 static addr_t sNextPageTableAddress = 0x7d000;
@@ -90,6 +91,7 @@
 #else
 
 static addr_t sNextPhysicalAddress = 0x100000;
+static addr_t sNextPhysicalKernelAddress = kIdentityMapEnd;
 static addr_t sNextVirtualAddress = KERNEL_LOAD_BASE + kMaxKernelSize;
 
 static addr_t sNextPageTableAddress = 0x90000;
@@ -100,7 +102,7 @@
 
 
 static addr_t
-get_next_virtual_address(size_t size)
+allocate_virtual(size_t size)
 {
 	addr_t address = sNextVirtualAddress;
 	sNextVirtualAddress += size;
@@ -110,21 +112,29 @@
 
 
 static addr_t
-get_next_physical_address(size_t size)
+allocate_physical(size_t size, bool inIdentityMap = true)
 {
 	if ((size % B_PAGE_SIZE) != 0)
 		panic("request for non-page-aligned physical memory!");
 
-	uint64 base;
+	addr_t* nextAddress = &sNextPhysicalKernelAddress;
+	if (inIdentityMap) {
+		nextAddress = &sNextPhysicalAddress;
+		if ((*nextAddress + size) > kIdentityMapEnd) {
+			panic("request too large for identity-map physical memory!");
+			return 0;
+		}
+	}
+
+	uint64 base = *nextAddress;
 	if (!get_free_address_range(gKernelArgs.physical_allocated_range,
-			gKernelArgs.num_physical_allocated_ranges, sNextPhysicalAddress,
-			size, &base)) {
+			gKernelArgs.num_physical_allocated_ranges, base, size, &base)) {
 		panic("Out of physical memory!");
 		return 0;
 	}
 
 	insert_physical_allocated_range(base, size);
-	sNextPhysicalAddress = base + size;
+	*nextAddress = base + size;
 		// TODO: Can overflow theoretically.
 
 	return base;
@@ -134,14 +144,14 @@
 static addr_t
 get_next_virtual_page()
 {
-	return get_next_virtual_address(B_PAGE_SIZE);
+	return allocate_virtual(B_PAGE_SIZE);
 }
 
 
 static addr_t
 get_next_physical_page()
 {
-	return get_next_physical_address(B_PAGE_SIZE);
+	return allocate_physical(B_PAGE_SIZE, false);
 }
 
 
@@ -154,7 +164,7 @@
 
 	addr_t address = sNextPageTableAddress;
 	if (address >= kPageTableRegionEnd)
-		return (uint32 *)get_next_physical_page();
+		return (uint32 *)allocate_physical(B_PAGE_SIZE);
 
 	sNextPageTableAddress += B_PAGE_SIZE;
 	return (uint32 *)address;
@@ -324,7 +334,7 @@
 	TRACE("init_page_directory\n");
 
 	// allocate a new pgdir
-	sPageDirectory = (uint32 *)get_next_physical_page();
+	sPageDirectory = (uint32 *)allocate_physical(B_PAGE_SIZE);
 	gKernelArgs.arch_args.phys_pgdir = (uint32)sPageDirectory;
 
 	// clear out the pgdir
@@ -636,7 +646,9 @@
 
 	gKernelArgs.physical_allocated_range[0].start = sNextPhysicalAddress;
 	gKernelArgs.physical_allocated_range[0].size = 0;
-	gKernelArgs.num_physical_allocated_ranges = 1;
+	gKernelArgs.physical_allocated_range[1].start = sNextPhysicalKernelAddress;
+	gKernelArgs.physical_allocated_range[1].size = 0;
+	gKernelArgs.num_physical_allocated_ranges = 2;
 		// remember the start of the allocated physical pages
 
 	init_page_directory();
@@ -818,13 +830,10 @@
 platform_allocate_heap_region(size_t size, void **_base)
 {
 	size = ROUNDUP(size, B_PAGE_SIZE);
-	addr_t base = get_next_physical_address(size);
+	addr_t base = allocate_physical(size);
 	if (base == 0)
 		return B_NO_MEMORY;
 
-	if ((base + size) > kIdentityMapEnd)
-		panic("platform_allocate_heap_region: region end is beyond identity map");
-
 	*_base = (void*)base;
 	return size;
 }