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, 9 insertions, 4 deletions

diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index a57d757eab6e..3271c0031a1b 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -62,8 +62,9 @@ static void push_guest_stack(struct lguest *lg, unsigned long *gstack, u32 val)
  * it). */
 static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err)
 {
-        unsigned long gstack;
+        unsigned long gstack, origstack;
         u32 eflags, ss, irq_enable;
+        unsigned long virtstack;
 
         /* There are two cases for interrupts: one where the Guest is already
          * in the kernel, and a more complex one where the Guest is in
@@ -71,8 +72,10 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err)
         if ((lg->regs->ss&0x3) != GUEST_PL) {
                 /* The Guest told us their kernel stack with the SET_STACK
                  * hypercall: both the virtual address and the segment */
-                gstack = guest_pa(lg, lg->esp1);
+                virtstack = lg->esp1;
                 ss = lg->ss1;
+
+                origstack = gstack = guest_pa(lg, virtstack);
                 /* We push the old stack segment and pointer onto the new
                  * stack: when the Guest does an "iret" back from the interrupt
                  * handler the CPU will notice they're dropping privilege
@@ -81,8 +84,10 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err)
                 push_guest_stack(lg, &gstack, lg->regs->esp);
         } else {
                 /* We're staying on the same Guest (kernel) stack. */
-                gstack = guest_pa(lg, lg->regs->esp);
+                virtstack = lg->regs->esp;
                 ss = lg->regs->ss;
+
+                origstack = gstack = guest_pa(lg, virtstack);
         }
 
         /* Remember that we never let the Guest actually disable interrupts, so
@@ -108,7 +113,7 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err)
         /* Now we've pushed all the old state, we change the stack, the code
          * segment and the address to execute. */
         lg->regs->ss = ss;
-        lg->regs->esp = gstack + lg->page_offset;
+        lg->regs->esp = virtstack + (gstack - origstack);
         lg->regs->cs = (__KERNEL_CS|GUEST_PL);
         lg->regs->eip = idt_address(lo, hi);