x86/mm/cpa: Add missing comment in populate_pdg()

In commit:

  21cbc2822aa1 ("x86/mm/cpa: Unbreak populate_pgd(): stop trying to deallocate failed PUDs")

I intended to add this comment, but I failed at using git.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/242baf8612394f4e31216f96d13c4d2e9b90d1b7.1469293159.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 2bc6ea153f76..47870a534877 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1091,6 +1091,11 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 
         ret = populate_pud(cpa, addr, pgd_entry, pgprot);
         if (ret < 0) {
+                /*
+                 * Leave the PUD page in place in case some other CPU or thread
+                 * already found it, but remove any useless entries we just
+                 * added to it.
+                 */
                 unmap_pud_range(pgd_entry, addr,
                                 addr + (cpa->numpages << PAGE_SHIFT));
                 return ret;