x86, cpa: no need to check alias for __set_pages_p/__set_pages_np

No alias checking needed for setting present/not-present mapping. Otherwise,
we may need to break large pages for 64-bit kernel text mappings (this adds to
complexity if we want to do this from atomic context especially, for ex:
with CONFIG_DEBUG_PAGEALLOC). Let's keep it simple!

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>

1 files changed, 16 insertions, 7 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 4b6968ba0864..162812b05d28 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1121,7 +1121,13 @@ static int __set_pages_p(struct page *page, int numpages)
                                 .mask_clr = __pgprot(0),
                                 .flags = 0};
 
-        return __change_page_attr_set_clr(&cpa, 1);
+        /*
+         * No alias checking needed for setting present flag. otherwise,
+         * we may need to break large pages for 64-bit kernel text
+         * mappings (this adds to complexity if we want to do this from
+         * atomic context especially). Let's keep it simple!
+         */
+        return __change_page_attr_set_clr(&cpa, 0);
 }
 
 static int __set_pages_np(struct page *page, int numpages)
@@ -1133,7 +1139,13 @@ static int __set_pages_np(struct page *page, int numpages)
                                 .mask_clr = __pgprot(_PAGE_PRESENT | _PAGE_RW),
                                 .flags = 0};
 
-        return __change_page_attr_set_clr(&cpa, 1);
+        /*
+         * No alias checking needed for setting not present flag. otherwise,
+         * we may need to break large pages for 64-bit kernel text
+         * mappings (this adds to complexity if we want to do this from
+         * atomic context especially). Let's keep it simple!
+         */
+        return __change_page_attr_set_clr(&cpa, 0);
 }
 
 void kernel_map_pages(struct page *page, int numpages, int enable)
@@ -1153,11 +1165,8 @@ void kernel_map_pages(struct page *page, int numpages, int enable)
 
         /*
          * The return value is ignored as the calls cannot fail.
-         * Large pages are kept enabled at boot time, and are
-         * split up quickly with DEBUG_PAGEALLOC. If a splitup
-         * fails here (due to temporary memory shortage) no damage
-         * is done because we just keep the largepage intact up
-         * to the next attempt when it will likely be split up:
+         * Large pages for identity mappings are not used at boot time
+         * and hence no memory allocations during large page split.
          */
         if (enable)
                 __set_pages_p(page, numpages);