Re: [PATCH 0/3] Fix some issues when looking up hugetlb page

From: Mike Kravetz <mike.kravetz@oracle.com>
To: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: akpm@linux-foundation.org, songmuchun@bytedance.com,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] Fix some issues when looking up hugetlb page
Date: Fri, 19 Aug 2022 17:08:23 -0700	[thread overview]
Message-ID: <YwAl948ny7AZEfT1@monkey> (raw)
In-Reply-To: <cover.1660902741.git.baolin.wang@linux.alibaba.com>

On 08/19/22 18:12, Baolin Wang wrote:
> Hi,
> 
> On ARM64 architecture, it can support CONT-PTE/PMD size hugetlb. When
> looking up hugetlb page by follow_page(), we will hold the incorrect
> pte/pmd lock for the CONT-PTE/PMD size hugetlb page, which will make
> the pte/pmd entry unstable even under the lock and cause some potential
> race issues. So considering the CONT-PTE/PMD size hugetlb, this patch set
> changes to use the correct function to get the correct pte/pmd entry lock
> to make the pte/pmd entry stable.

Thank you for looking at this.

I often get confused by arm64 CONT-PTE/PMD layout, so my understanding may be
wrong.  Can we use the PMD page lock for locking both CONT-PTE and CONT-PMD
entries?  Again, I may be confused by the CONT-* page table layout, but it
seems these would all be referenced via that same PMD page of the page table.
Or, perhaps CONT-PMD can span multiple PMD pages?

If we can use PMD page for locking, this would be much finer grain that
lock in the mm.
-- 
Mike Kravetz