x86, mm: Hold mm->page_table_lock while doing vmalloc_sync

Take mm->page_table_lock while syncing the vmalloc region.  This prevents
a race with the Xen pagetable pin/unpin code, which expects that the
page_table_lock is already held.  If this race occurs, then Xen can see
an inconsistent page type (a page can either be read/write or a pagetable
page, and pin/unpin converts it between them), which will cause either
the pin or the set_p[gm]d to fail; either will crash the kernel.

vmalloc_sync_all() should be called rarely, so this extra use of
page_table_lock should not interfere with its normal users.

The mm pointer is stashed in the pgd page's index field, as that won't
be otherwise used for pgds.

Reported-by: Ian Campbell <ian.cambell@eu.citrix.com>
Originally-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <4CB88A4C.1080305@goop.org>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 2d0a33bd2971..ada823a13c7c 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -28,6 +28,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 extern spinlock_t pgd_lock;
 extern struct list_head pgd_list;
 
+extern struct mm_struct *pgd_page_get_mm(struct page *page);
+
 #ifdef CONFIG_PARAVIRT
 #include <asm/paravirt.h>
 #else  /* !CONFIG_PARAVIRT */