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>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index a125109446dc..39f64c95de18 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -216,9 +216,10 @@ static int emulate_insn(struct lguest *lg)
          * guest_pa just subtracts the Guest's page_offset. */
         unsigned long physaddr = guest_pa(lg, lg->regs->eip);
 
-        /* The guest_pa() function only works for Guest kernel addresses, but
-         * that's all we're trying to do anyway. */
-        if (lg->regs->eip < lg->page_offset)
+        /* This must be the Guest kernel trying to do something, not userspace!
+         * The bottom two bits of the CS segment register are the privilege
+         * level. */
+        if ((lg->regs->cs & 3) != GUEST_PL)
                 return 0;
 
         /* Decoding x86 instructions is icky. */