Boot with virtual == physical to get closer to native Linux.

1) This allows us to get alot closer to booting bzImages.

2) It means we don't have to know page_offset.

3) The Guest needs to modify the boot pagetables to create the
   PAGE_OFFSET mapping before jumping to C code.

4) guest_pa() walks the page tables rather than using page_offset.

5) We don't use page_offset to figure out whether to emulate: it was
   always kinda quesationable, and won't work for instructions done
   before remapping (bzImage unpacking in particular).

6) We still want the kernel address for tlb flushing: have the initial
   hypercall give us that, too.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

include/linux/lguest.h

@@ -44,11 +44,14 @@ struct lguest_data
 	unsigned long reserve_mem;
 	/* KHz for the TSC clock. */
 	u32 tsc_khz;
+	/* Page where the top-level pagetable is */
+	unsigned long pgdir;
 
 /* Fields initialized by the Guest at boot: */
 	/* Instruction range to suppress interrupts even if enabled */
 	unsigned long noirq_start, noirq_end;
-
+	/* Address above which page tables are all identical. */
+	unsigned long kernel_address;
 	/* The vector to try to use for system calls (0x40 or 0x80). */
 	unsigned int syscall_vec;
 };