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Subject: Re: [PATCH v8 2/2] mm: remove zap_page_range and change callers to
 use zap_vma_range
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <20221108011910.350887-3-mike.kravetz@oracle.com>
Date:   Thu, 10 Nov 2022 13:09:43 -0800
Cc:     Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        David Hildenbrand <david@redhat.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Peter Xu <peterx@redhat.com>, Rik van Riel <riel@surriel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>
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References: <20221108011910.350887-1-mike.kravetz@oracle.com>
 <20221108011910.350887-3-mike.kravetz@oracle.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>
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On Nov 7, 2022, at 5:19 PM, Mike Kravetz <mike.kravetz@oracle.com> wrote:

> zap_page_range was originally designed to unmap pages within an address
> range that could span multiple vmas.  However, today all callers of
> zap_page_range pass a range entirely within a single vma.  In addition,
> the mmu notification call within zap_page range is not correct as it
> should be vma specific.
> 
> Instead of fixing zap_page_range, change all callers to use zap_vma_range
> as it is designed for ranges within a single vma.

I understand the argument about mmu notifiers being broken (which is of
course fixable).

But, are the callers really able to guarantee that the ranges are all in a
single VMA? I am not familiar with the users, but how for instance
tcp_zerocopy_receive() can guarantee that no one did some mprotect() of some
sorts that caused the original VMA to be split?