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Date: Sun, 2 Sep 2018 19:52:02 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Benjamin Herrenschmidt <benh@...nel.crashing.org> Cc: Jiri Kosina <jikos@...nel.org>, Jürgen Groß <jgross@...e.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...e.com>, Naoya Horiguchi <n-horiguchi@...jp.nec.com>, Michael Ellerman <mpe@...erman.id.au>, Will Deacon <will.deacon@....com> Subject: Re: Access to non-RAM pages On Sun, Sep 2, 2018 at 7:47 PM Linus Torvalds <torvalds@...ux-foundation.org> wrote: > > The comment actually does talk about it, although the comment also > claims that the cs read would use load_unaligned_zeropad(), which it > no longer does (now it only does the read_word_at_a_time). IOW, look at commit 12f8ad4b0533 ("vfs: clean up __d_lookup_rcu() and dentry_cmp() interfaces") for why the zeropad went away for the cs access (but the comment wasn't updated). And then bfe7aa6c39b1 ("fs/dcache: Use read_word_at_a_time() in dentry_string_cmp()") did the "let's make KASAN happy thing. And yes, the word-at-a-time code actually matters a lot for certain loads. The "copy-and-hash" thing for path components ends up being pretty critical in all the pathname handling. Linus
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