linux-kernel - Re: [PATCH 3/5] mm/migrate.c: fix potential indeterminate pte entry in migrate_vma_insert

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Date:   Tue, 23 Mar 2021 11:26:43 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     jglisse@...hat.com, shy828301@...il.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/5] mm/migrate.c: fix potential indeterminate pte entry
 in migrate_vma_insert_page()

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@...wei.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