lguest: use a special 1:1 linear pagetable mode until first switch.

The Host used to create some page tables for the Guest to use at the
top of Guest memory; it would then tell the Guest where this was.  In
particular, it created linear mappings for 0 and 0xC0000000 addresses
because lguest used to switch to its real page tables quite late in
boot.

However, since d50d8fe19 Linux initialized boot page tables in
head_32.S even before the "are we lguest?" boot jump.  So, now we can
simplify things: the Host pagetable code assumes 1:1 linear mapping
until it first calls the LHCALL_NEW_PGTABLE hypercall, which we now do
before we reach C code.

This also means that the Host doesn't need to know anything about the
Guest's PAGE_OFFSET.  (Non-Linux guests might not even have such a
thing).

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

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 9136411fadd5..295df06e6590 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -59,6 +59,8 @@ struct lg_cpu {
 
         struct lguest_pages *last_pages;
 
+        /* Initialization mode: linear map everything. */
+        bool linear_pages;
         int cpu_pgd; /* Which pgd this cpu is currently using */
 
         /* If a hypercall was asked for, this points to the arguments. */