linux-kernel - Re: [PATCH] mm: fix hugetlb page unmap count balance issue

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Message-Id: <20230512140353.8b95e8cb024c8e7a1a3b03c1@linux-foundation.org>
Date:   Fri, 12 May 2023 14:03:53 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Junxiao Chang <junxiao.chang@...el.com>
Cc:     kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        jmarchan@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, mike.kravetz@...cle.com,
        muchun.song@...ux.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@...el.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.