Re: [PATCH v2 1/2] mm: Call arch_swap_restore() from do_swap_page()

[David Hildenbrand]

On 16.05.23 04:35, Peter Collingbourne wrote:
> Commit c145e0b47c77 ("mm: streamline COW logic in do_swap_page()") moved
> the call to swap_free() before the call to set_pte_at(), which meant that
> the MTE tags could end up being freed before set_pte_at() had a chance
> to restore them. Fix it by adding a call to the arch_swap_restore() hook
> before the call to swap_free().
>
> Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
> Link: https://linux-review.googlesource.com/id/I6470efa669e8bd2f841049b8c61020c510678965
> Cc: <stable@xxxxxxxxxxxxxxx> # 6.1
> Fixes: c145e0b47c77 ("mm: streamline COW logic in do_swap_page()")
> Reported-by: Qun-wei Lin (林群崴) <Qun-wei.Lin@xxxxxxxxxxxx>
> Link: https://lore.kernel.org/all/5050805753ac469e8d727c797c2218a9d780d434.camel@xxxxxxxxxxxx/
> ---
> v2:
> - Call arch_swap_restore() directly instead of via arch_do_swap_page()
>
>   mm/memory.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 01a23ad48a04..a2d9e6952d31 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3914,6 +3914,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>   		}
>   	}
>   
> +	/*
> +	 * Some architectures may have to restore extra metadata to the page
> +	 * when reading from swap. This metadata may be indexed by swap entry
> +	 * so this must be called before swap_free().
> +	 */
> +	arch_swap_restore(entry, folio);
> +
>   	/*
>   	 * Remove the swap entry and conditionally try to free up the swapcache.
>   	 * We're already holding a reference on the page but haven't mapped it

Looks much better to me, thanks :)

... staring at unuse_pte(), I suspect it also doesn't take care of MTE 
tags and needs fixing?

--
Thanks,

David / dhildenb