[PATCH] x86_64: actively synchronize vmalloc area when registering certain callbacks

While the modular aspect of the respective i386 patch doesn't apply to
x86-64 (as the top level page directory entry is shared between modules
and the base kernel), handlers registered with register_die_notifier()
are still under similar constraints for touching ioremap()ed or
vmalloc()ed memory. The likelihood of this problem becoming visible is
of course significantly lower, as the assigned virtual addresses would
have to cross a 2**39 byte boundary. This is because the callback gets
invoked
(a) in the page fault path before the top level page table propagation
gets carried out (hence a fault to propagate the top level page table
entry/entries mapping to module's code/data would nest infinitly) and
(b) in the NMI path, where nested faults must absolutely not happen,
since otherwise the IRET from the nested fault re-enables NMIs,
potentially resulting in nested NMI occurences.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/asm-x86_64/pgalloc.h b/include/asm-x86_64/pgalloc.h
index 08cad2482bcb..43d4c333a8b1 100644
--- a/include/asm-x86_64/pgalloc.h
+++ b/include/asm-x86_64/pgalloc.h
@@ -45,12 +45,39 @@ static inline void pud_free (pud_t *pud)
         free_page((unsigned long)pud);
 }
 
+static inline void pgd_list_add(pgd_t *pgd)
+{
+        struct page *page = virt_to_page(pgd);
+
+        spin_lock(&pgd_lock);
+        page->index = (pgoff_t)pgd_list;
+        if (pgd_list)
+                pgd_list->private = (unsigned long)&page->index;
+        pgd_list = page;
+        page->private = (unsigned long)&pgd_list;
+        spin_unlock(&pgd_lock);
+}
+
+static inline void pgd_list_del(pgd_t *pgd)
+{
+        struct page *next, **pprev, *page = virt_to_page(pgd);
+
+        spin_lock(&pgd_lock);
+        next = (struct page *)page->index;
+        pprev = (struct page **)page->private;
+        *pprev = next;
+        if (next)
+                next->private = (unsigned long)pprev;
+        spin_unlock(&pgd_lock);
+}
+
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
         unsigned boundary;
         pgd_t *pgd = (pgd_t *)__get_free_page(GFP_KERNEL|__GFP_REPEAT);
         if (!pgd)
                 return NULL;
+        pgd_list_add(pgd);
         /*
          * Copy kernel pointers in from init.
          * Could keep a freelist or slab cache of those because the kernel
@@ -67,6 +94,7 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 static inline void pgd_free(pgd_t *pgd)
 {
         BUG_ON((unsigned long)pgd & (PAGE_SIZE-1));
+        pgd_list_del(pgd);
         free_page((unsigned long)pgd);
 }