Re: [PATCH 3/5] mm/migrate.c: fix potential indeterminate pte entry in migrate_vma_insert_page()

[David Hildenbrand <david@redhat.com>]

On 20.03.21 10:36, Miaohe Lin wrote:
> If the zone device page does not belong to un-addressable device memory,
> the variable entry will be uninitialized and lead to indeterminate pte
> entry ultimately. Fix this unexpectant case and warn about it.

s/unexpectant/unexpected/

> 
> Fixes: df6ad69838fc ("mm/device-public-memory: device memory cache coherent with CPU")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>   mm/migrate.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 20a3bf75270a..271081b014cb 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2972,6 +2972,13 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
>   
>   			swp_entry = make_device_private_entry(page, vma->vm_flags & VM_WRITE);
>   			entry = swp_entry_to_pte(swp_entry);
> +		} else {
> +			/*
> +			 * For now we only support migrating to un-addressable
> +			 * device memory.
> +			 */
> +			WARN_ON(1);
> +			goto abort;

Fix it by crashing the kernel with panic_on_warn? :)

If this case can actual happen, than no WARN_ON() - rather a 
pr_warn_once(). If this case cannot happen, why do we even care (it's 
not a fix then)?


-- 
Thanks,

David / dhildenb