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From: Andrey Konovalov <andreyknvl@google.com>
To: Marco Elver <elver@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alexander Potapenko <glider@google.com>,
	 "H. Peter Anvin" <hpa@zytor.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	 Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Andy Lutomirski <luto@kernel.org>,
	 Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christoph Lameter <cl@linux.com>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	 Dmitry Vyukov <dvyukov@google.com>,
	Eric Dumazet <edumazet@google.com>,
	 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Hillf Danton <hdanton@sina.com>,  Ingo Molnar <mingo@redhat.com>,
	Jann Horn <jannh@google.com>,
	 Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Jonathan Corbet <corbet@lwn.net>,
	 Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Kees Cook <keescook@chromium.org>,
	 Mark Rutland <mark.rutland@arm.com>,
	Pekka Enberg <penberg@kernel.org>,
	 Peter Zijlstra <peterz@infradead.org>,
	SeongJae Park <sjpark@amazon.com>,
	 Thomas Gleixner <tglx@linutronix.de>,
	Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.org>,
	 "the arch/x86 maintainers" <x86@kernel.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	 LKML <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure
Date: Tue, 29 Sep 2020 16:01:52 +0200	[thread overview]
Message-ID: <CAAeHK+ycOZ1E1P8PGbZizYUE7EGkj90tJ8et0Ki79LZMAkJWXA@mail.gmail.com> (raw)
In-Reply-To: <CANpmjNOFpFkrSMFezcBFJODwBK5vRi8sSEzS3AvyFu3Y0ZqgVA@mail.gmail.com>

On Tue, Sep 29, 2020 at 3:49 PM Marco Elver <elver@google.com> wrote:
>
> On Tue, 29 Sep 2020 at 15:48, Andrey Konovalov <andreyknvl@google.com> wrote:
> > On Tue, Sep 29, 2020 at 3:11 PM Marco Elver <elver@google.com> wrote:
> > >
> > > On Tue, Sep 29, 2020 at 02:42PM +0200, Andrey Konovalov wrote:
> > > [...]
> > > > > +        */
> > > > > +       index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
> > > >
> > > > Why do we subtract 1 here? We do have the metadata entry reserved for something?
> > >
> > > Above the declaration of __kfence_pool it says:
> > >
> > >         * We allocate an even number of pages, as it simplifies calculations to map
> > >         * address to metadata indices; effectively, the very first page serves as an
> > >         * extended guard page, but otherwise has no special purpose.
> > >
> > > Hopefully that clarifies the `- 1` here.
> >
> > So there are two guard pages at the beginning and only then a page
> > that holds an object?
>
> Yes, correct.

OK, I see. This isn't directly clear from the comment though, at least for me :)


  reply	other threads:[~2020-09-29 14:02 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-21 13:26 [PATCH v3 00/10] KFENCE: A low-overhead sampling-based memory safety error detector Marco Elver
2020-09-21 13:26 ` [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure Marco Elver
2020-09-25 11:23   ` SeongJae Park
2020-09-25 11:31     ` Marco Elver
2020-09-29 12:42   ` Andrey Konovalov
2020-09-29 13:11     ` Marco Elver
2020-09-29 13:48       ` Andrey Konovalov
2020-09-29 13:49         ` Marco Elver
2020-09-29 14:01           ` Andrey Konovalov [this message]
2020-09-29 14:24   ` Mark Rutland
2020-09-29 14:51     ` Marco Elver
2020-09-29 15:05       ` Mark Rutland
2020-10-05 16:00         ` Alexander Potapenko
2020-10-05 16:49           ` Jann Horn
2020-09-29 15:51     ` Alexander Potapenko
2020-10-01 18:11       ` Mark Rutland
2020-09-21 13:26 ` [PATCH v3 02/10] x86, kfence: enable KFENCE for x86 Marco Elver
2020-09-21 13:26 ` [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64 Marco Elver
2020-09-21 14:31   ` Will Deacon
2020-09-21 14:58     ` Alexander Potapenko
2020-09-21 15:37       ` Alexander Potapenko
2020-09-21 17:43         ` Will Deacon
2020-09-22  9:56           ` Marco Elver
2020-09-29 13:53             ` Mark Rutland
2020-09-29 16:52               ` Alexander Potapenko
2020-09-25 15:25     ` Alexander Potapenko
2020-09-29 14:02       ` Mark Rutland
2020-10-01 11:24         ` Alexander Potapenko
2020-10-01 17:57           ` Mark Rutland
2020-10-08  9:40             ` Marco Elver
2020-10-08 10:45               ` Mark Rutland
2020-10-14 19:12                 ` Marco Elver
2020-10-15 13:39                   ` Mark Rutland
2020-10-15 14:15                     ` Marco Elver
2020-09-28 11:53     ` Marco Elver
2020-09-29 14:27   ` Mark Rutland
2020-09-29 17:04     ` Alexander Potapenko
2020-09-21 13:26 ` [PATCH v3 04/10] mm, kfence: insert KFENCE hooks for SLAB Marco Elver
2020-09-21 13:26 ` [PATCH v3 05/10] mm, kfence: insert KFENCE hooks for SLUB Marco Elver
2020-09-21 13:26 ` [PATCH v3 06/10] kfence, kasan: make KFENCE compatible with KASAN Marco Elver
2020-09-29 12:20   ` Andrey Konovalov
2020-09-29 13:13     ` Alexander Potapenko
2020-09-21 13:26 ` [PATCH v3 07/10] kfence, kmemleak: make KFENCE compatible with KMEMLEAK Marco Elver
2020-09-21 13:26 ` [PATCH v3 08/10] kfence, lockdep: make KFENCE compatible with lockdep Marco Elver
2020-09-21 13:26 ` [PATCH v3 09/10] kfence, Documentation: add KFENCE documentation Marco Elver
2020-09-21 13:26 ` [PATCH v3 10/10] kfence: add test suite Marco Elver
2020-09-21 17:13   ` Paul E. McKenney
2020-09-21 17:37     ` Marco Elver
2020-09-21 17:48       ` Paul E. McKenney
2020-09-21 13:38 ` [PATCH v3 00/10] KFENCE: A low-overhead sampling-based memory safety error detector Dmitry Vyukov

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