Re: Kernel writes to RAM it doesn't own on 2.4.24

[Ross Biro <ross.biro@gmail.com>]

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> I believe what I did was to save a copy of the e820 maps for later,
> and then take then take the first free address as the max of the first
> free address from the user supplied map and the bios supplied map.
> I'll send out a patch on Tuesday.

Here's the changes to setup.c.  I haven't check to see if it's
complete, but I did the diff from a working 2.4.18-kernel.  You need
to apply this patch in arch/i386/kernel.

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--- /home/rossb/local/linux-2.4.18/arch/i386/kernel/setup.c	2003-09-23 19:55:13.000000000 -0700
+++ setup.c	2004-03-24 10:20:56.000000000 -0800
@@ -113,6 +113,17 @@
 #include <asm/dma.h>
 #include <asm/mpspec.h>
 #include <asm/mmu_context.h>
+
+#define PFN_UP(x)	(((x) + PAGE_SIZE-1) >> PAGE_SHIFT)
+#define PFN_DOWN(x)	((x) >> PAGE_SHIFT)
+#define PFN_PHYS(x)	((x) << PAGE_SHIFT)
+
+/*
+ * Reserved space for vmalloc and iomap - defined in asm/page.h
+ */
+#define MAXMEM_PFN	PFN_DOWN(MAXMEM)
+#define MAX_NONPAE_PFN	(1 << 20)
+
 /*
  * Machine setup..
  */
@@ -121,6 +132,8 @@
 struct cpuinfo_x86 boot_cpu_data = { 0, 0, 0, 0, -1, 1, 0, 0, -1 };
 
 unsigned long mmu_cr4_features;
+unsigned long num_e820physpages;
+unsigned long num_e820_nonpae_physpages;
 
 /*
  * Bus types ..
@@ -151,6 +164,7 @@
 };
 
 struct e820map e820;
+struct e820map bios_e820;
 
 unsigned char aux_device_present;
 
@@ -710,11 +724,44 @@
 	char c = ' ', *to = command_line, *from = COMMAND_LINE;
 	int len = 0;
 	int usermem = 0;
+        int i;
+        unsigned long max_pfn;
 
 	/* Save unparsed command line copy for /proc/cmdline */
 	memcpy(saved_command_line, COMMAND_LINE, COMMAND_LINE_SIZE);
 	saved_command_line[COMMAND_LINE_SIZE-1] = '\0';
 
+        /* Compute this here in case the user wants to know it later. */
+	max_pfn = 0;
+        max_low_pfn = 0;
+	for (i = 0; i < e820.nr_map; i++) {
+		unsigned long start, end;
+		/* RAM? */
+		if (e820.map[i].type != E820_RAM &&
+                    e820.map[i].type != E820_ACPI)
+			continue;
+
+		start = PFN_UP(e820.map[i].addr);
+		end = PFN_DOWN(e820.map[i].addr + e820.map[i].size);
+		if (start >= end)
+			continue;
+                if (end > MAX_NONPAE_PFN) {
+                     if (start < MAX_NONPAE_PFN) {
+                          max_low_pfn = MAX_NONPAE_PFN;
+                     }
+                } else {
+                     if (end > max_low_pfn) {
+                          max_low_pfn = end;
+                     }
+                }
+		if (end > max_pfn)
+			max_pfn = end;
+	}
+
+        num_e820physpages = max_pfn;
+        num_e820_nonpae_physpages = max_low_pfn;
+        memcpy(&bios_e820, &e820, sizeof(e820));
+
 	for (;;) {
 		/*
 		 * "mem=nopentium" disables the 4MB page tables.
@@ -783,6 +830,7 @@
 {
 	unsigned long bootmap_size, low_mem_size;
 	unsigned long start_pfn, max_pfn, max_low_pfn;
+        unsigned long e820_low_mem_size;
 	int i;
 
 #ifdef CONFIG_VISWS
@@ -822,16 +870,6 @@
 
 	parse_mem_cmdline(cmdline_p);
 
-#define PFN_UP(x)	(((x) + PAGE_SIZE-1) >> PAGE_SHIFT)
-#define PFN_DOWN(x)	((x) >> PAGE_SHIFT)
-#define PFN_PHYS(x)	((x) << PAGE_SHIFT)
-
-/*
- * Reserved space for vmalloc and iomap - defined in asm/page.h
- */
-#define MAXMEM_PFN	PFN_DOWN(MAXMEM)
-#define MAX_NONPAE_PFN	(1 << 20)
-
 	/*
 	 * partially used pages are not usable - thus
 	 * we are rounding upwards:
@@ -1032,8 +1070,16 @@
 
 	/* Tell the PCI layer not to allocate too close to the RAM area.. */
 	low_mem_size = ((max_low_pfn << PAGE_SHIFT) + 0xfffff) & ~0xfffff;
+
+        e820_low_mem_size = ((num_e820_nonpae_physpages << PAGE_SHIFT) + 
+                             0xfffff) & ~0xfffff;
+
+	if (e820_low_mem_size > pci_mem_start)
+             pci_mem_start = e820_low_mem_size;
+        
 	if (low_mem_size > pci_mem_start)
 		pci_mem_start = low_mem_size;
+                     
 
 #ifdef CONFIG_VT
 #if defined(CONFIG_VGA_CONSOLE)