Re: [PATCH 4.17] x86/mm: Don't free P4D table when it is folded at runtime

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jul 02, 2018 at 11:45:36AM +0300, Andrey Ryabinin wrote:
> From: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>

Huh?  I didn't write this patch.

> 
> 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@virtuozzo.com>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: stable@vger.kernel.org # 4.17
> Fixes: 98219dda2ab5 ("x86/mm: Fold p4d page table layer at runtime")
> Link: http://lkml.kernel.org/r/20180625102427.15015-1-aryabinin@virtuozzo.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
>  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;
> +

Did you test build this patch?

Please do so, and be careful about author attribution, again, I did not
write this patch.

greg k-h