On Mon, Jul 02, 2018 at 11:48:28AM +0300, Andrey Ryabinin wrote:
> commit 0e311d237d7f3022b7dafb639b42541bfb42fe94 upstream.
>
> 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>
> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> ---
>
> Changes since v1:
> - Fix wrong "From:" field
>
> 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 263c142a6a6c..f65e9e1cea4c 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;
> +
Again, did you actually test-build this? What changed from the original
patch which blew the build up into little tiny pieces?
greg k-h
