Introduce guest mem offset, static link example launcher

In order to avoid problematic special linking of the Launcher, we give
the Host an offset: this means we can use any memory region in the
Launcher as Guest memory rather than insisting on mmap() at 0.

The result is quite pleasing: a number of casts are replaced with
simple additions.

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

1 files changed, 13 insertions, 10 deletions

diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 80d1b58c7698..816d4d12a801 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -1,9 +1,9 @@
 /*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
  * controls and communicates with the Guest.  For example, the first write will
- * tell us the memory size, pagetable, entry point and kernel address offset.
- * A read will run the Guest until a signal is pending (-EINTR), or the Guest
- * does a DMA out to the Launcher.  Writes are also used to get a DMA buffer
- * registered by the Guest and to send the Guest an interrupt. :*/
+ * tell us the Guest's memory layout, pagetable, entry point and kernel address
+ * offset.  A read will run the Guest until something happens, such as a signal
+ * or the Guest doing a DMA out to the Launcher.  Writes are also used to get a
+ * DMA buffer registered by the Guest and to send the Guest an interrupt. :*/
 #include <linux/uaccess.h>
 #include <linux/miscdevice.h>
 #include <linux/fs.h>
@@ -142,9 +142,11 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
         return run_guest(lg, (unsigned long __user *)user);
 }
 
-/*L:020 The initialization write supplies 4 32-bit values (in addition to the
+/*L:020 The initialization write supplies 5 32-bit values (in addition to the
  * 32-bit LHREQ_INITIALIZE value).  These are:
  *
+ * base: The start of the Guest-physical memory inside the Launcher memory.
+ *
  * pfnlimit: The highest (Guest-physical) page number the Guest should be
  * allowed to access.  The Launcher has to live in Guest memory, so it sets
  * this to ensure the Guest can't reach it.
@@ -166,7 +168,7 @@ static int initialize(struct file *file, const u32 __user *input)
          * Guest. */
         struct lguest *lg;
         int err, i;
-        u32 args[4];
+        u32 args[5];
 
         /* We grab the Big Lguest lock, which protects the global array
          * "lguests" and multiple simultaneous initializations. */
@@ -194,8 +196,9 @@ static int initialize(struct file *file, const u32 __user *input)
 
         /* Populate the easy fields of our "struct lguest" */
         lg->guestid = i;
-        lg->pfn_limit = args[0];
-        lg->page_offset = args[3];
+        lg->mem_base = (void __user *)(long)args[0];
+        lg->pfn_limit = args[1];
+        lg->page_offset = args[4];
 
         /* We need a complete page for the Guest registers: they are accessible
          * to the Guest and we can only grant it access to whole pages. */
@@ -210,13 +213,13 @@ static int initialize(struct file *file, const u32 __user *input)
         /* Initialize the Guest's shadow page tables, using the toplevel
          * address the Launcher gave us.  This allocates memory, so can
          * fail. */
-        err = init_guest_pagetable(lg, args[1]);
+        err = init_guest_pagetable(lg, args[2]);
         if (err)
                 goto free_regs;
 
         /* Now we initialize the Guest's registers, handing it the start
          * address. */
-        setup_regs(lg->regs, args[2]);
+        setup_regs(lg->regs, args[3]);
 
         /* There are a couple of GDT entries the Guest expects when first
          * booting. */