[tip:x86/urgent] x86/mm: Don't free P4D table when it is folded at runtime

[tip-bot for Andrey Ryabinin]

Commit-ID:  0e311d237d7f3022b7dafb639b42541bfb42fe94
Gitweb:     https://git.kernel.org/tip/0e311d237d7f3022b7dafb639b42541bfb42fe94
Author:     Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
AuthorDate: Mon, 25 Jun 2018 13:24:27 +0300
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 26 Jun 2018 09:21:48 +0200

x86/mm: Don't free P4D table when it is folded at runtime

When the P4D page table layer is folded at runtime, the p4d_free()
should do nothing, the same as in <asm-generic/pgtable-nop4d.h>.

It seems this bug should cause double-free in efi_call_phys_epilog(),
but I don't know how to trigger that code path, so I can't confirm that
by testing.

Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 4.17
Fixes: 98219dda2ab5 ("x86/mm: Fold p4d page table layer at runtime")
Link: http://lkml.kernel.org/r/20180625102427.15015-1-aryabinin@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/pgalloc.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
index ada6410fd2ec..fbd578daa66e 100644
--- a/arch/x86/include/asm/pgalloc.h
+++ b/arch/x86/include/asm/pgalloc.h
@@ -184,6 +184,9 @@ static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr)
 
 static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
 {
+	if (!pgtable_l5_enabled())
+		return;
+
 	BUG_ON((unsigned long)p4d & (PAGE_SIZE-1));
 	free_page((unsigned long)p4d);
 }