From f0000078c32898973f6f79f3f6c24a1fde59e0fd Mon Sep 17 00:00:00 2001
From: Ben Gras <ben@minix3.org>
Date: Thu, 18 Dec 2008 14:30:55 +0000
Subject: [PATCH] make kernel leave a page-sized gap in its code and data to
 not be mapped in if so configured.

---
 include/minix/com.h       |  1 +
 include/minix/config.h    |  3 +++
 kernel/arch/i386/memory.c | 25 +++++++++++++++++++++++--
 kernel/system/do_vmctl.c  |  5 +++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/include/minix/com.h b/include/minix/com.h
index 5358c1784..4e93a76d4 100755
--- a/include/minix/com.h
+++ b/include/minix/com.h
@@ -593,6 +593,7 @@
 #define VMCTL_MEMREQ_REPLY	15
 #define VMCTL_INCSP		16
 #define VMCTL_STACKTRACE	17
+#define VMCTL_NOPAGEZERO	18
 
 /*===========================================================================*
  *                Messages for the Reincarnation Server 		     *
diff --git a/include/minix/config.h b/include/minix/config.h
index 8bac14ba4..dcfeb4326 100755
--- a/include/minix/config.h
+++ b/include/minix/config.h
@@ -95,4 +95,7 @@
 #define SPROFILE          1    /* statistical profiling */
 #define CPROFILE          0    /* call profiling */
 
+/* Compile kernel so that first page of code and data can be unmapped. */
+#define VM_KERN_NOPAGEZERO      1       
+
 #endif /* _CONFIG_H */
diff --git a/kernel/arch/i386/memory.c b/kernel/arch/i386/memory.c
index e02008868..16c6cb294 100644
--- a/kernel/arch/i386/memory.c
+++ b/kernel/arch/i386/memory.c
@@ -45,6 +45,7 @@ PUBLIC void vm_init(void)
 	u32_t entry;
 	unsigned pages;
 	struct proc* rp;
+	struct proc *sys = proc_addr(SYSTEM);
 
 	if (!vm_size)
 		minix_panic("i386_vm_init: no space for page tables", NO_NUM);
@@ -77,6 +78,12 @@ PUBLIC void vm_init(void)
 			I386_VM_PRESENT;
 		if (phys_mem >= vm_mem_high)
 			entry= 0;
+#if VM_KERN_NOPAGEZERO
+		if (phys_mem == (sys->p_memmap[T].mem_phys << CLICK_SHIFT) ||
+		    phys_mem == (sys->p_memmap[D].mem_phys << CLICK_SHIFT)) {
+			entry = 0;
+		}
+#endif
 		phys_put32(vm_pt_base + p*I386_VM_PT_ENT_SIZE, entry);
 	}
 
@@ -471,6 +478,7 @@ PUBLIC int vm_checkrange(struct proc *caller, struct proc *target,
 
 	vmassert(vm_running);
 
+
 	/* If caller has had a reply to this request, return it. */
 	if(RTS_ISSET(caller, VMREQUEST)) {
 		if(caller->p_vmrequest.who == target->p_endpoint) {
@@ -522,8 +530,9 @@ PUBLIC int vm_checkrange(struct proc *caller, struct proc *target,
 			target->p_name, target->p_endpoint, v, wrfl, flags, phys);
 		}
 
-		if(checkonly)
+		if(checkonly) {
 			return VMSUSPEND;
+		}
 
 		/* This range is not OK for this process. Set parameters
 		 * of the request and notify VM about the pending request.
@@ -544,7 +553,19 @@ PUBLIC int vm_checkrange(struct proc *caller, struct proc *target,
 		/* Connect caller on vmrequest wait queue. */
 		caller->p_vmrequest.nextrequestor = vmrequest;
 		vmrequest = caller;
-		soft_notify(VM_PROC_NR);
+		if(!caller->p_vmrequest.nextrequestor) {
+			int n = 0;
+			struct proc *vmr;
+			for(vmr = vmrequest; vmr; vmr = vmr->p_vmrequest.nextrequestor)
+				n++;
+			soft_notify(VM_PROC_NR);
+#if 0
+			kprintf("(%d) ", n);
+			kprintf("%d/%d ",
+				caller->p_endpoint, target->p_endpoint);
+			util_stacktrace();
+#endif
+		}
 
 #if 0
 		kprintf("SYSTEM: vm_checkrange: range bad for "
diff --git a/kernel/system/do_vmctl.c b/kernel/system/do_vmctl.c
index bceeed639..2628f1e2a 100644
--- a/kernel/system/do_vmctl.c
+++ b/kernel/system/do_vmctl.c
@@ -11,6 +11,7 @@
 #include "../vm.h"
 #include "../debug.h"
 #include <minix/type.h>
+#include <minix/config.h>
 
 /*===========================================================================*
  *				do_vmctl				     *
@@ -92,6 +93,10 @@ kprintf("SYSTEM: request %d:0x%lx-0x%lx, wrflag %d, failed\n",
 		}
 #endif
 		return OK;
+#if VM_KERN_NOPAGEZERO
+	case VMCTL_NOPAGEZERO:
+		return OK;
+#endif
 	case VMCTL_STACKTRACE:
 		kprintf("vmctl stacktrace ");
 		proc_stacktrace(p);
-- 
2.44.0