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Message-ID: <1a4e51a4d2ed51e7ae1ff55bd4da6a47fad7c0bf.camel@sipsolutions.net>
Subject: Re: [PATCH v2 2/2] UML: add support for KASAN under x86_64
From:   Johannes Berg <johannes@sipsolutions.net>
To:     David Gow <davidgow@google.com>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        Patricia Alfonso <trishalfonso@google.com>,
        Jeff Dike <jdike@addtoit.com>,
        Richard Weinberger <richard@nod.at>,
        anton.ivanov@cambridgegreys.com,
        Dmitry Vyukov <dvyukov@google.com>,
        Brendan Higgins <brendanhiggins@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc:     kasan-dev <kasan-dev@googlegroups.com>,
        linux-um@lists.infradead.org, LKML <linux-kernel@vger.kernel.org>,
        Daniel Latypov <dlatypov@google.com>, linux-mm@kvack.org
Date:   Sun, 29 May 2022 19:04:08 +0200
In-Reply-To: <20220527185600.1236769-2-davidgow@google.com>
References: <20220527185600.1236769-1-davidgow@google.com>
         <20220527185600.1236769-2-davidgow@google.com>
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On Fri, 2022-05-27 at 11:56 -0700, David Gow wrote:
>=20
> The UML-specific KASAN initializer uses mmap to map the roughly 2.25TB

You say 2.25TB here, and
=20
> +config KASAN_SHADOW_OFFSET
> +	hex
> +	depends on KASAN
> +	default 0x100000000000
> +	help
> +	  This is the offset at which the ~2.25TB of shadow memory is

here too, of course.

But I notice that I get ~16TB address space use when running,

> +/* used in kasan_mem_to_shadow to divide by 8 */
> +#define KASAN_SHADOW_SCALE_SHIFT 3
> +
> +#ifdef CONFIG_X86_64
> +#define KASAN_HOST_USER_SPACE_END_ADDR 0x00007fffffffffffUL
> +/* KASAN_SHADOW_SIZE is the size of total address space divided by 8 */
> +#define KASAN_SHADOW_SIZE ((KASAN_HOST_USER_SPACE_END_ADDR + 1) >> \
> +			KASAN_SHADOW_SCALE_SHIFT)

because this ends up being 0x100000000000, i.e. 16 TiB.

Is that intentional? Was something missed? Maybe
KASAN_HOST_USER_SPACE_END_ADDR was too big?

It doesn't really matter, but I guess then the documentation should be
updated.

johannes