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Date:   Thu, 21 Sep 2023 17:25:44 +0100
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Subject: Re: [PATCH] mm: hugetlb: kill set_huge_swap_pte_at()
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To:     Qi Zheng <zhengqi.arch@bytedance.com>, mike.kravetz@oracle.com,
        songmuchun@bytedance.com, akpm@linux-foundation.org,
        catalin.marinas@arm.com, will@kernel.org
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
References: <20220626145717.53572-1-zhengqi.arch@bytedance.com>
From:   Ryan Roberts <ryan.roberts@arm.com>
In-Reply-To: <20220626145717.53572-1-zhengqi.arch@bytedance.com>
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On 26/06/2022 15:57, Qi Zheng wrote:
> The commit e5251fd43007 ("mm/hugetlb: introduce set_huge_swap_pte_at()
> helper") add set_huge_swap_pte_at() to handle swap entries on
> architectures that support hugepages consisting of contiguous ptes.
> And currently the set_huge_swap_pte_at() is only overridden by arm64.
> 
> The set_huge_swap_pte_at() provide a sz parameter to help determine
> the number of entries to be updated. But in fact, all hugetlb swap
> entries contain pfn information, so we can find the corresponding
> folio through the pfn recorded in the swap entry, then the folio_size()
> is the number of entries that need to be updated.
> 
> And considering that users will easily cause bugs by ignoring the
> difference between set_huge_swap_pte_at() and set_huge_pte_at().
> Let's handle swap entries in set_huge_pte_at() and remove the
> set_huge_swap_pte_at(), then we can call set_huge_pte_at()
> anywhere, which simplifies our coding.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Hi,

FYI, I discovered a bug in v6.6-rc1 that causes a kernel panic, which I believe
is caused by this change. I've posted a fix along with a detailed explanation at
[1].

[1]
https://lore.kernel.org/linux-arm-kernel/20230921162007.1630149-1-ryan.roberts@arm.com/

Thanks,
Ryan