lguest: remove RESERVE_MEM constant.

We can use switcher_addr directly.

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

1 files changed, 11 insertions, 7 deletions

diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index a2454a24a10c..27cbb186a911 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -63,10 +63,8 @@
  */
 #ifdef CONFIG_X86_PAE
 #define SWITCHER_PMD_INDEX      (PTRS_PER_PMD - 1)
-#define RESERVE_MEM             2U
 #define CHECK_GPGD_MASK         _PAGE_PRESENT
 #else
-#define RESERVE_MEM             4U
 #define CHECK_GPGD_MASK         _PAGE_TABLE
 #endif
 
@@ -977,15 +975,21 @@ int init_guest_pagetable(struct lguest *lg)
 /*H:508 When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
 void page_table_guest_data_init(struct lg_cpu *cpu)
 {
+        /*
+         * We tell the Guest that it can't use the virtual addresses
+         * used by the Switcher.  This trick is equivalent to 4GB -
+         * switcher_addr.
+         */
+        u32 top = ~switcher_addr + 1;
+
         /* We get the kernel address: above this is all kernel memory. */
         if (get_user(cpu->lg->kernel_address,
-                &cpu->lg->lguest_data->kernel_address)
+                     &cpu->lg->lguest_data->kernel_address)
                 /*
-                 * We tell the Guest that it can't use the top 2 or 4 MB
-                 * of virtual addresses used by the Switcher.
+                 * We tell the Guest that it can't use the top virtual
+                 * addresses (used by the Switcher).
                  */
-                || put_user(RESERVE_MEM * 1024 * 1024,
-                            &cpu->lg->lguest_data->reserve_mem)) {
+            || put_user(top, &cpu->lg->lguest_data->reserve_mem)) {
                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
                 return;
         }