linux-kernel - Re: [PATCH v5 3/4] x86/xen/time: setup vcpu 0 time info page

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Date:   Mon, 2 Oct 2017 14:44:20 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Joao Martins <joao.m.martins@...cle.com>,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Juergen Gross <jgross@...e.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v5 3/4] x86/xen/time: setup vcpu 0 time info page


> +
> +static void xen_setup_vsyscall_time_info(void)
> +{
> +	struct vcpu_register_time_memory_area t;
> +	struct pvclock_vsyscall_time_info *ti;
> +	int ret;


In the previous version you'd return immediately if
PVCLOCK_TSC_STABLE_BIT was not set. Don't you still need to check this?
Especially give...


> +
> +	ti = (struct pvclock_vsyscall_time_info *)get_zeroed_page(GFP_KERNEL);
> +	if (!ti)
> +		return;
> +
> +	t.addr.v = &ti->pvti;
> +
> +	ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area, 0, &t);
> +	if (ret) {
> +		pr_notice("xen: VCLOCK_PVCLOCK not supported (err %d)\n", ret);
> +		free_page((unsigned long)ti);
> +		return;
> +	}
> +
> +	/*
> +	 * If primary time info had this bit set, secondary should too since

... this comment?

-boris

> +	 * it's the same data on both just different memory regions. But we
> +	 * still check it in case hypervisor is buggy.
> +	 */
> +	if (!(ti->pvti.flags & PVCLOCK_TSC_STABLE_BIT)) {
> +		t.addr.v = NULL;
> +		ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area,
> +					 0, &t);
> +		if (!ret)
> +			free_page((unsigned long)ti);
> +
> +		pr_notice("xen: VCLOCK_PVCLOCK not supported (tsc unstable)\n");
> +		return;
> +	}
> +
> +	xen_clock = ti;
> +	pvclock_set_pvti_cpu0_va(xen_clock);
> +
> +	xen_clocksource.archdata.vclock_mode = VCLOCK_PVCLOCK;
> +}
> +
>