Bug 54418

	There is a problem in setting page protection in function
	vm_map_protect().
	When we set for example max_protection to VM_PROT_READ and
	after that we will try do change max_protection to VM_PROT_ALL
	there is no chance to do that, because of bogus check. This 'if'
	doesn't check if we set max_protection or just protection and
	denieds all increasing max_protection tries.
	Problem doesn't affect FreeBSD directly, because such situation
	never occurs, but for 3rd-party kernel modules this could be importent.
	For example, for my module - cerb - where I need to do operations
	on VM pages, it is very important and this bug provoke 'Bus error's
	in some situations.

Fix: This patch fix this.
How-To-Repeat: 	This sample kernel module shows the problem. It is for FreeBSD 4.x,
	but simlar could be prepared for 5.x.

#include <sys/param.h>

#include <sys/proc.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/systm.h>

#include <sys/lock.h>
#include <vm/vm.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>

static int
mod(struct module *module, int cmd, void *arg)
{
	vm_map_t map = &curproc->p_vmspace->vm_map;
	vm_offset_t start, end;
	int error = 0;

	switch (cmd) {
	case MOD_LOAD:
		end = start = (vm_offset_t)curproc->p_vmspace->vm_daddr +
		    ctob(curproc->p_vmspace->vm_dsize);
		start--;
		error = vm_map_protect(map, start, end, VM_PROT_READ, TRUE);
		printf("ERROR1: %d\n", error);
		error = vm_map_protect(map, start, end, VM_PROT_ALL, TRUE);
		/* Here should be 2 which means KERN_PROTECTION_FAILURE. */
		printf("ERROR2: %d\n", error);
		error = 0;
		printf("testmod loaded.\n");
		break;
	case MOD_UNLOAD:
		printf("testmod unloaded.\n");
		break;
	default:
		error = EINVAL;
		break;
	}

	return (error);
}

static moduledata_t testmod_mod =
{
	"testmod",
	mod,
	NULL
};

DECLARE_MODULE(testmod, testmod_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);