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SubjectRE: [PATCH] mm: fix hugetlb page unmap count balance issue
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Thank you for review it! We only reproduced this hugetlb mapping issue with QEMU command which opens udmabuf driver(drivers/dma-buf/udmabuf.c).
I agree with you, it is better to map huge page with a pmd instead of a pte. 😊

-----Original Message-----
From: Andrew Morton <akpm@linux-foundation.org>
Sent: Saturday, May 13, 2023 5:04 AM
To: Chang, Junxiao <junxiao.chang@intel.com>
Cc: kirill.shutemov@linux.intel.com; Hocko, Michal <mhocko@suse.com>; jmarchan@redhat.com; linux-mm@kvack.org; linux-kernel@vger.kernel.org; mike.kravetz@oracle.com; muchun.song@linux.dev
Subject: Re: [PATCH] mm: fix hugetlb page unmap count balance issue

On Fri, 12 May 2023 15:20:36 +0800 Junxiao Chang <junxiao.chang@intel.com> wrote:

> hugetlb page usually is mapped with pmd, but occasionally it might be
> mapped with pte. QEMU can use udma-buf to create host dmabufs for
> guest framebuffers. When QEMU is launched with parameter "hugetlb=on",
> udmabuffer driver maps hugetlb page with pte in page fault handler.

Are there any other situations in which a hugetlb page is mapped in this fashion?

If not, can QEMU be changed to map with a pmd?

So we get one less weird special case in MM.
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