lguest: map Switcher below fixmap.

Now we've adjusted all the code, we can simply set switcher_addr to
wherever it needs to go below the fixmaps, rather than asserting that
it should be so.

With large NR_CPUS and PAE, people were hitting the "mapping switcher
would thwack fixmap" message.

Reported-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 5 insertions, 10 deletions

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 7e1d7ee36478..0bf1e4edf04d 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -83,18 +83,13 @@ static __init int map_switcher(void)
                 }
         }
 
-        switcher_addr = SWITCHER_ADDR;
-
         /*
-         * First we check that the Switcher won't overlap the fixmap area at
-         * the top of memory.  It's currently nowhere near, but it could have
-         * very strange effects if it ever happened.
+         * We place the Switcher underneath the fixmap area, which is the
+         * highest virtual address we can get.  This is important, since we
+         * tell the Guest it can't access this memory, so we want its ceiling
+         * as high as possible.
          */
-        if (switcher_addr + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
-                err = -ENOMEM;
-                printk("lguest: mapping switcher would thwack fixmap\n");
-                goto free_pages;
-        }
+        switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE;
 
         /*
          * Now we reserve the "virtual memory area" we want.  We might