Re: [Qemu-devel] [Qemu-arm] [PATCH 1/3] tcg: Fix off-by-one in assert in page_set_flags - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
To: Richard Henderson <rth@twiddle.net>, qemu-devel@nongnu.org
Cc: aurelien@aurel32.net, riku.voipio@iki.fi, laurent@vivier.eu,
	qemu-arm@nongnu.org
Subject: Re: [Qemu-devel] [Qemu-arm] [PATCH 1/3] tcg: Fix off-by-one in assert in page_set_flags
Date: Sat, 8 Jul 2017 14:10:45 -0300	[thread overview]
Message-ID: <66bdbcf1-dd15-1e7e-bc30-d80ae6e88ffb@amsat.org> (raw)
In-Reply-To: <20170708025030.15845-2-rth@twiddle.net>

On 07/07/2017 11:50 PM, Richard Henderson wrote:
> Most of the users of page_set_flags offset (page, page + len) as
> the end points.  One might consider this an error, since the other
> users do supply an endpoint as the last byte of the region.
> 
> However, the first thing that page_set_flags does is round end UP
> to the start of the next page.  Which means computing page + len - 1
> is in the end pointless.  Therefore, accept this usage and do not
> assert when given the exact size of the vm as the endpoint.
> 
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>   accel/tcg/translate-all.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index dfb9f0d..57578a4 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -2068,7 +2068,7 @@ void page_set_flags(target_ulong start, target_ulong end, int flags)
>          guest address space.  If this assert fires, it probably indicates
>          a missing call to h2g_valid.  */
>   #if TARGET_ABI_BITS > L1_MAP_ADDR_SPACE_BITS
> -    assert(end < ((target_ulong)1 << L1_MAP_ADDR_SPACE_BITS));
> +    assert(end <= ((target_ulong)1 << L1_MAP_ADDR_SPACE_BITS));

worth adding a comment /* end rounded up */ ?

anyway for this tricky catch:
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

>   #endif
>       assert(start < end);
>       assert_memory_lock();
> 