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

[tip-bot for Andy Lutomirski]

Commit-ID:  55920d31f1e3fea06702c74271dd56c4fc9b70ca
Gitweb:     http://git.kernel.org/tip/55920d31f1e3fea06702c74271dd56c4fc9b70ca
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Sat, 23 Jul 2016 09:59:28 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 23 Jul 2016 21:17:10 +0200

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@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/242baf8612394f4e31216f96d13c4d2e9b90d1b7.1469293159.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/mm/pageattr.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 2bc6ea1..47870a5 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;