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SubjectRe: [PATCH v3 1/3] mm/swapfile: unuse_pte can map random data if swap read fails
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Hi, Miaohe,

On Sun, 2022-04-24 at 17:11 +0800, Miaohe Lin wrote:
> There is a bug in unuse_pte(): when swap page happens to be unreadable,
> page filled with random data is mapped into user address space. In case
> of error, a special swap entry indicating swap read fails is set to the
> page table. So the swapcache page can be freed and the user won't end up
> with a permanently mounted swap because a sector is bad. And if the page
> is accessed later, the user process will be killed so that corrupted data
> is never consumed. On the other hand, if the page is never accessed, the
> user won't even notice it.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> ---
>  include/linux/swap.h | 7 ++++++-
>  include/linux/swapops.h | 10 ++++++++++
>  mm/memory.c | 5 ++++-
>  mm/swapfile.c | 11 +++++++++++
>  4 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 5553189d0215..b82c196d8867 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -55,6 +55,10 @@ static inline int current_is_kswapd(void)
>   * actions on faults.
>   */
>
> +#define SWP_SWAPIN_ERROR_NUM 1
> +#define SWP_SWAPIN_ERROR (MAX_SWAPFILES + SWP_HWPOISON_NUM + \
> + SWP_MIGRATION_NUM + SWP_DEVICE_NUM + \
> + SWP_PTE_MARKER_NUM)
>
>

It appears wasteful to use another swap device number. Is it possible
to use a special swap offset? For example, 0 or -1?

Best Regards,
Huang, Ying


[snip]


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