linux-kernel - Re: [PATCH v2 7/7] xen/arm: set the system time in Xen via the XENPF

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Date:	Tue, 10 Nov 2015 13:39:44 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	Ian.Campbell@...rix.com
Subject: Re: [PATCH v2 7/7] xen/arm: set the system time in Xen via the XENPF_settime64 hypercall

On Tuesday 10 November 2015 11:57:55 Stefano Stabellini wrote:
> +       op.u.settime64.nsecs = now.tv_nsec;
> +       op.u.settime64.system_time = arch_timer_read_counter() * (u64)NSEC_PER_SEC;
> +       do_div(op.u.settime64.system_time, arch_timer_get_rate());

NSEC_PER_SEC is a large number, doesn't that multiplication overflow the
64-bit system_time variable?

> +       printk("GTOD: Setting to %llu.%u at %llu\n",

				   %llu.%09u

so you get the leading zeroes.

> +              op.u.settime64.secs,
> +              op.u.settime64.nsecs,
> +              op.u.settime64.system_time);
> +       (void)HYPERVISOR_platform_op(&op);

	Arnd
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