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Date:   Sun, 10 Jan 2021 09:14:43 -0800
From:   Andi Kleen <ak@linux.intel.com>
To:     Miaohe Lin <linmiaohe@huawei.com>
Cc:     akpm@linux-foundation.org, tglx@linutronix.de,
        dave.hansen@intel.com, jpoimboe@redhat.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: Fix potential pte_unmap_unlock pte error
Message-ID: <20210110171443.GC1914459@tassilo.jf.intel.com>
References: <20210109080118.20885-1-linmiaohe@huawei.com>
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On Sat, Jan 09, 2021 at 03:01:18AM -0500, Miaohe Lin wrote:
> Since commit 42e4089c7890 ("x86/speculation/l1tf: Disallow non privileged
> high MMIO PROT_NONE mappings"), when the first pfn modify is not allowed,
> we would break the loop with pte unchanged. Then the wrong pte - 1 would
> be passed to pte_unmap_unlock.

Thanks.

While the fix is correct, I'm not sure if it actually is a real bug. Is there
any architecture that would do something else than unlocking the underlying
page?  If it's just the underlying page then it should be always the same
page, so no bug.

That said of course the change is the right thing for main line, but probably doesn't
need to be backported.

-Andi