Subject: Re: [PATCH v12 05/31] mm: prepare for FAULT_FLAG_SPECULATIVE

From: Jerome Glisse <[email-masked]>
Date: Thu, 18 Apr 2019 18:04:15 -0400

On Tue, Apr 16, 2019 at 03:44:56PM +0200, Laurent Dufour wrote:
> From: Peter Zijlstra <[email-masked]>
> 
> When speculating faults (without holding mmap_sem) we need to validate
> that the vma against which we loaded pages is still valid when we're
> ready to install the new PTE.
> 
> Therefore, replace the pte_offset_map_lock() calls that (re)take the
> PTL with pte_map_lock() which can fail in case we find the VMA changed
> since we started the fault.
> 
> Signed-off-by: Peter Zijlstra (Intel) <[email-masked]>
> 
> [Port to 4.12 kernel]
> [Remove the comment about the fault_env structure which has been
>  implemented as the vm_fault structure in the kernel]
> [move pte_map_lock()'s definition upper in the file]
> [move the define of FAULT_FLAG_SPECULATIVE later in the series]
> [review error path in do_swap_page(), do_anonymous_page() and
>  wp_page_copy()]
> Signed-off-by: Laurent Dufour <[email-masked]>

Reviewed-by: Jérôme Glisse <[email-masked]>

> ---
>  mm/memory.c | 87 +++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 58 insertions(+), 29 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index c6ddadd9d2b7..fc3698d13cb5 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2073,6 +2073,13 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
>  }
>  EXPORT_SYMBOL_GPL(apply_to_page_range);
>  
> +static inline bool pte_map_lock(struct vm_fault *vmf)

I am not fan of the name maybe pte_offset_map_lock_if_valid() ? But
that just a taste thing. So feel free to ignore this comment.

> +{
> +	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
> +				       vmf->address, &vmf->ptl);
> +	return true;
> +}
> +
>  /*
>   * handle_pte_fault chooses page fault handler according to an entry which was
>   * read non-atomically.  Before making any commitment, on those architectures