x86, mm: Make DEBUG_VIRTUAL work earlier in boot

The KVM code has some repeated bugs in it around use of __pa() on
per-cpu data.  Those data are not in an area on which using
__pa() is valid.  However, they are also called early enough in
boot that __vmalloc_start_set is not set, and thus the
CONFIG_DEBUG_VIRTUAL debugging does not catch them.

This adds a check to also verify __pa() calls against max_low_pfn,
which we can use earler in boot than is_vmalloc_addr().  However,
if we are super-early in boot, max_low_pfn=0 and this will trip
on every call, so also make sure that max_low_pfn is set before
we try to use it.

With this patch applied, CONFIG_DEBUG_VIRTUAL will actually
catch the bug I was chasing (and fix later in this series).

I'd love to find a generic way so that any __pa() call on percpu
areas could do a BUG_ON(), but there don't appear to be any nice
and easy ways to check if an address is a percpu one.  Anybody
have ideas on a way to do this?

Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20130122212430.F46F8159@kernel.stglabs.ibm.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 0eb572eda40..2610bd93c89 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -560,10 +560,10 @@ int kernel_map_sync_memtype(u64 base, unsigned long size, unsigned long flags)
 {
 	unsigned long id_sz;
 
-	if (base >= __pa(high_memory))
+	if (base > __pa(high_memory-1))
 		return 0;
 
-	id_sz = (__pa(high_memory) < base + size) ?
+	id_sz = (__pa(high_memory-1) <= base + size) ?
 				__pa(high_memory) - base :
 				size;