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From: Greg KH on 12 Mar 2010 19:50
2.6.32-stable review patch. If anyone has any objections, please let me know.

----------------
From: Ian Campbell <ian.campbell(a)citrix.com>

commit 817a824b75b1475f1b067c8cee318c7b4d66fcde upstream.

There's a path in the pagefault code where the kernel deliberately
breaks its own locking rules by kmapping a high pte page without
holding the pagetable lock (in at least page_check_address). This
breaks Xen's ability to track the pinned/unpinned state of the
page. There does not appear to be a viable workaround for this
behaviour so simply disable HIGHPTE for all Xen guests.

Signed-off-by: Ian Campbell <ian.campbell(a)citrix.com>
LKML-Reference: <1267204562-11844-1-git-send-email-ian.campbell(a)citrix.com>
Cc: Jeremy Fitzhardinge <jeremy(a)goop.org>
Cc: Ingo Molnar <mingo(a)elte.hu>
Cc: Pasi Kärkkäinen <pasik(a)iki.fi>
Cc: <xen-devel(a)lists.xensource.com>
Signed-off-by: H. Peter Anvin <hpa(a)zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
arch/x86/xen/enlighten.c | 7 +++++++
arch/x86/xen/mmu.c | 11 ++++++-----
2 files changed, 13 insertions(+), 5 deletions(-)

--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -48,6 +48,7 @@
#include <asm/traps.h>
#include <asm/setup.h>
#include <asm/desc.h>
+#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/reboot.h>
@@ -1092,6 +1093,12 @@ asmlinkage void __init xen_start_kernel(

__supported_pte_mask |= _PAGE_IOMAP;

+ /*
+ * Prevent page tables from being allocated in highmem, even
+ * if CONFIG_HIGHPTE is enabled.
+ */
+ __userpte_alloc_gfp &= ~__GFP_HIGHMEM;
+
#ifdef CONFIG_X86_64
/* Work out if we support NX */
check_efer();
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1432,14 +1432,15 @@ static void *xen_kmap_atomic_pte(struct
{
pgprot_t prot = PAGE_KERNEL;

+ /*
+ * We disable highmem allocations for page tables so we should never
+ * see any calls to kmap_atomic_pte on a highmem page.
+ */
+ BUG_ON(PageHighMem(page));
+
if (PagePinned(page))
prot = PAGE_KERNEL_RO;

- if (0 && PageHighMem(page))
- printk("mapping highpte %lx type %d prot %s\n",
- page_to_pfn(page), type,
- (unsigned long)pgprot_val(prot) & _PAGE_RW ? "WRITE" : "READ");
-
return kmap_atomic_prot(page, type, prot);
}
#endif


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