From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Rich Felker <dalias@libc.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Linux-sh list <linux-sh@vger.kernel.org>,
James Hogan <jhogan@kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Khalid Aziz <khalid.aziz@oracle.com>,
Nicholas Piggin <npiggin@gmail.com>,
linux-mips@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
Paul Burton <paul.burton@mips.com>,
Paul Mackerras <paulus@samba.org>,
Andrey Konovalov <andreyknvl@google.com>,
sparclinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
"David S. Miller" <davem@davemloft.net>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 03/16] mm: simplify gup_fast_permitted
Date: Sat, 1 Jun 2019 09:14:17 -0700 [thread overview]
Message-ID: <CAHk-=whusWKhS=SYoC9f9HjVmPvR5uP51Mq=ZCtktqTBT2qiBw@mail.gmail.com> (raw)
In-Reply-To: <20190601074959.14036-4-hch@lst.de>
On Sat, Jun 1, 2019 at 12:50 AM Christoph Hellwig <hch@lst.de> wrote:
>
> Pass in the already calculated end value instead of recomputing it, and
> leave the end > start check in the callers instead of duplicating them
> in the arch code.
Good cleanup, except it's wrong.
> - if (nr_pages <= 0)
> + if (end < start)
> return 0;
You moved the overflow test to generic code - good.
You removed the sign and zero test on nr_pages - bad.
The zero test in particular is _important_ - the GUP range operators
know and depend on the fact that they are passed a non-empty range.
The sign test it less so, but is definitely appropriate. It might be
even better to check that the "<< PAGE_SHIFT" doesn't overflow in
"long", of course, but with callers being supposed to be trusted, the
sign test at least checks for stupid underflow issues.
So at the very least that "(end < start)" needs to be "(end <=
start)", but honestly, I think the sign of the nr_pages should be
continued to be checked.
Linus
next prev parent reply other threads:[~2019-06-01 16:17 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-01 7:49 RFC: switch the remaining architectures to use generic GUP v2 Christoph Hellwig
2019-06-01 7:49 ` [PATCH 01/16] uaccess: add untagged_addr definition for other arches Christoph Hellwig
2019-06-03 15:16 ` Khalid Aziz
2019-06-04 7:27 ` Christoph Hellwig
2019-06-04 11:46 ` Andrey Konovalov
2019-06-01 7:49 ` [PATCH 02/16] mm: use untagged_addr() for get_user_pages_fast addresses Christoph Hellwig
2019-06-01 7:49 ` [PATCH 03/16] mm: simplify gup_fast_permitted Christoph Hellwig
2019-06-01 16:14 ` Linus Torvalds [this message]
2019-06-03 7:41 ` Christoph Hellwig
2019-06-03 16:08 ` Linus Torvalds
2019-06-03 17:02 ` Linus Torvalds
2019-06-04 7:26 ` Christoph Hellwig
2019-06-01 7:49 ` [PATCH 04/16] mm: lift the x86_32 PAE version of gup_get_pte to common code Christoph Hellwig
2019-06-01 7:49 ` [PATCH 05/16] MIPS: use the generic get_user_pages_fast code Christoph Hellwig
2019-06-01 7:49 ` [PATCH 06/16] sh: add the missing pud_page definition Christoph Hellwig
2019-06-01 7:49 ` [PATCH 07/16] sh: use the generic get_user_pages_fast code Christoph Hellwig
2019-06-01 7:49 ` [PATCH 08/16] sparc64: add the missing pgd_page definition Christoph Hellwig
2019-06-01 16:28 ` Linus Torvalds
2019-06-03 7:44 ` Christoph Hellwig
2019-06-01 7:49 ` [PATCH 09/16] sparc64: define untagged_addr() Christoph Hellwig
2019-06-01 7:49 ` [PATCH 10/16] sparc64: use the generic get_user_pages_fast code Christoph Hellwig
2019-06-02 7:39 ` Hillf Danton
2019-06-03 7:44 ` Christoph Hellwig
2019-06-01 7:49 ` [PATCH 11/16] mm: rename CONFIG_HAVE_GENERIC_GUP to CONFIG_HAVE_FAST_GUP Christoph Hellwig
2019-06-01 7:49 ` [PATCH 12/16] mm: consolidate the get_user_pages* implementations Christoph Hellwig
2019-06-06 6:01 ` John Hubbard
2019-06-06 6:20 ` Christoph Hellwig
2019-06-06 7:44 ` John Hubbard
2019-06-01 7:49 ` [PATCH 13/16] mm: validate get_user_pages_fast flags Christoph Hellwig
2019-06-01 7:49 ` [PATCH 14/16] mm: move the powerpc hugepd code to mm/gup.c Christoph Hellwig
2019-06-01 7:49 ` [PATCH 15/16] mm: switch gup_hugepte to use try_get_compound_head Christoph Hellwig
2019-06-01 7:49 ` [PATCH 16/16] mm: mark the page referenced in gup_hugepte Christoph Hellwig
2019-06-01 23:46 ` RFC: switch the remaining architectures to use generic GUP v2 David Miller
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