Re: [PATCH v4 1/3] mm: Call arch_swap_restore() from do_swap_page()

[Will Deacon]

Hi Peter,

On Mon, May 22, 2023 at 05:43:08PM -0700, 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>
> Closes: https://lore.kernel.org/all/5050805753ac469e8d727c797c2218a9d780d434.camel@xxxxxxxxxxxx/
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> Acked-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Reviewed-by: Steven Price <steven.price@xxxxxxx>
> Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> ---
> 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 f69fbc251198..fc25764016b3 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3932,6 +3932,13 @@ 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

It looks like the intention is for this patch to land in 6.4, whereas the
other two in the series could go in later, right? If so, I was expecting
Andrew to pick this one up but he's not actually on CC. I've added him now,
but you may want to send this as a separate fix so it's obvious what needs
picking up for this cycle.

Cheers,

Will