Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings

[Matt Fleming <matt@codeblueprint.co.uk>]

On Wed, 24 Feb, at 08:39:56AM, Andy Lutomirski wrote:
> 
> OK, although a comment might be nice.

Something like this?

---
>From ac40fc0269d4d8cc9051982c177ee140d6e1b761 Mon Sep 17 00:00:00 2001
From: Matt Fleming <matt@codeblueprint.co.uk>
Date: Thu, 25 Feb 2016 15:54:50 +0000
Subject: [PATCH] x86/mm/pat: Document the (currently) EFI-only code path

It's not at all obvious that populate_pgd() and friends are only
executed when mapping EFI virtual memory regions or that no other
pageattr callers pass a ->pgd value.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
---
 arch/x86/mm/pageattr.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 14c38ae80409..8fee5b6f8f66 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1125,8 +1125,14 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 static int __cpa_process_fault(struct cpa_data *cpa, unsigned long vaddr,
 			       int primary)
 {
-	if (cpa->pgd)
+	if (cpa->pgd) {
+		/*
+		 * Right now, we only execute this code path when mapping
+		 * the EFI virtual memory map regions, no other users
+		 * provide a ->pgd value. This may change in the future.
+		 */
 		return populate_pgd(cpa, vaddr);
+	}
 
 	/*
 	 * Ignore all non primary paths.
-- 
2.6.2