x86, cpa: srlz cpa(), global flush tlb after splitting big page and before doing cpa

Do a global flush tlb after splitting the large page and before we do the
actual change page attribute in the PTE.

With out this, we violate the TLB application note, which says
    "The TLBs may contain both ordinary and large-page translations for
     a 4-KByte range of linear addresses. This may occur if software
     modifies the paging structures so that the page size used for the
     address range changes. If the two translations differ with respect
     to page frame or attributes (e.g., permissions), processor behavior
     is undefined and may be implementation-specific."

And also serialize cpa() (for !DEBUG_PAGEALLOC which uses large identity
mappings) using cpa_lock. So that we don't allow any other cpu, with stale
large tlb entries change the page attribute in parallel to some other cpu
splitting a large page entry along with changing the attribute.
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: arjan@linux.intel.com
Cc: venkatesh.pallipadi@intel.com
Cc: jeremy@goop.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/pageattr.c

@@ -35,6 +35,14 @@ struct cpa_data {
 	int		curpage;
 };
 
+/*
+ * Serialize cpa() (for !DEBUG_PAGEALLOC which uses large identity mappings)
+ * using cpa_lock. So that we don't allow any other cpu, with stale large tlb
+ * entries change the page attribute in parallel to some other cpu
+ * splitting a large page entry along with changing the attribute.
+ */
+static DEFINE_SPINLOCK(cpa_lock);
+
 #define CPA_FLUSHTLB 1
 #define CPA_ARRAY 2
 
@@ -453,7 +461,13 @@ static int split_large_page(pte_t *kpte, unsigned long address)
 	unsigned int i, level;
 	pte_t *pbase, *tmp;
 	pgprot_t ref_prot;
-	struct page *base = alloc_pages(GFP_KERNEL, 0);
+	struct page *base;
+
+	if (!debug_pagealloc)
+		spin_unlock(&cpa_lock);
+	base = alloc_pages(GFP_KERNEL, 0);
+	if (!debug_pagealloc)
+		spin_lock(&cpa_lock);
 	if (!base)
 		return -ENOMEM;
 
@@ -594,7 +608,25 @@ static int __change_page_attr(struct cpa_data *cpa, int primary)
 	 */
 	err = split_large_page(kpte, address);
 	if (!err) {
-		cpa->flags |= CPA_FLUSHTLB;
+		/*
+	 	 * Do a global flush tlb after splitting the large page
+	 	 * and before we do the actual change page attribute in the PTE.
+	 	 *
+	 	 * With out this, we violate the TLB application note, that says
+	 	 * "The TLBs may contain both ordinary and large-page
+		 *  translations for a 4-KByte range of linear addresses. This
+		 *  may occur if software modifies the paging structures so that
+		 *  the page size used for the address range changes. If the two
+		 *  translations differ with respect to page frame or attributes
+		 *  (e.g., permissions), processor behavior is undefined and may
+		 *  be implementation-specific."
+	 	 *
+	 	 * We do this global tlb flush inside the cpa_lock, so that we
+		 * don't allow any other cpu, with stale tlb entries change the
+		 * page attribute in parallel, that also falls into the
+		 * just split large page entry.
+	 	 */
+		flush_tlb_all();
 		goto repeat;
 	}
 
@@ -686,7 +718,11 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
 		if (cpa->flags & CPA_ARRAY)
 			cpa->numpages = 1;
 
+		if (!debug_pagealloc)
+			spin_lock(&cpa_lock);
 		ret = __change_page_attr(cpa, checkalias);
+		if (!debug_pagealloc)
+			spin_unlock(&cpa_lock);
 		if (ret)
 			return ret;