From: Will Deacon <will@kernel.org>
To: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Qi Zheng <qi.zheng@linux.dev>,
akpm@linux-foundation.org, catalin.marinas@arm.com,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, muchun.song@linux.dev,
pasha.tatashin@soleen.com, wangkefeng.wang@huawei.co
Subject: Re: [PATCH] arm64: mm: use ptep_clear() instead of pte_clear() in clear_flush()
Date: Fri, 11 Aug 2023 12:21:07 +0100 [thread overview]
Message-ID: <20230811112107.GE6993@willie-the-truck> (raw)
In-Reply-To: <CAOgjDMi6kTZUjEianbO670RQxJ8=JhHxkeci9NspSCRT5rPhYw@mail.gmail.com>
On Fri, Aug 11, 2023 at 07:16:20PM +0800, Qi Zheng wrote:
> Will Deacon <[1]will@kernel.org>于2023年8月11日 周五19:03写道：
>
> On Thu, Aug 10, 2023 at 09:32:41AM +0000, Qi Zheng wrote:
> > From: Qi Zheng <[2]zhengqi.arch@bytedance.com>
> >
> > In clear_flush(), the original pte may be a present entry, so we
> should
> > use ptep_clear() to let page_table_check track the pte clearing
> operation,
> > otherwise it may cause false positive in subsequent set_pte_at().
>
> Isn't this true for most users of pte_clear()? There are some in the
> core
> code, so could they trigger the false positive as well?
>
> No, the PTE entry in other places where pte_clear() is used is non-present
> PTE.
> The page_table_check does not does track the pte operation in this case,
> so it will not cause false positives.
Are you sure? For example, the call from flush_all_zero_pkmaps() in
highmem.c really looks like it's clearing a valid entry. Not that arm64
cares about highmem, but still.
Will
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next prev parent reply other threads:[~2023-08-11 11:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-10 9:32 [PATCH] arm64: mm: use ptep_clear() instead of pte_clear() in clear_flush() Qi Zheng
2023-08-11 2:38 ` Qi Zheng
2023-08-11 11:03 ` Will Deacon
[not found] ` <CAOgjDMi6kTZUjEianbO670RQxJ8=JhHxkeci9NspSCRT5rPhYw@mail.gmail.com>
2023-08-11 11:21 ` Will Deacon [this message]
[not found] ` <CAOgjDMgVZXbEeA6O2yPR9N27JWCMNR3D7cgHJbmbfYYUdKF3eQ@mail.gmail.com>
2023-08-21 20:21 ` Andrew Morton
2023-08-22 2:23 ` Qi Zheng
2023-08-22 9:58 ` Will Deacon
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