[PATCH 03/40] x86/mm/pat: Document the (currently) EFI-only code path

Matt Fleming
2016-04-25T20:19:09Z

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 01be9ec3bf79..a1f0e1d0ddc2 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.
--
2.7.3