linux-kernel - Re: [PATCH RFC 2/3] x86/xen/time: setup vcpu 0 time info page

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Date:	Mon, 4 Jan 2016 11:07:53 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Joao Martins <joao.m.martins@...cle.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xen.org
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH RFC 2/3] x86/xen/time: setup vcpu 0 time info page

On 12/28/2015 04:52 PM, Joao Martins wrote:
> +
> +static int xen_setup_vsyscall_time_info(int cpu)
> +{
> +	struct pvclock_vsyscall_time_info *ti;
> +	struct vcpu_register_time_memory_area t;
> +	struct pvclock_vcpu_time_info *pvti;
> +	unsigned long mem;
> +	int ret, size;
> +	u8 flags;
> +
> +	ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area,
> +				 cpu, NULL);
> +	if (ret == -ENOSYS) {
> +		pr_debug("xen: vcpu_time_info placement not supported\n");
> +		return -ENOTSUPP;
> +	}

I don't think this is necessary.

> +
> +	size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info));
> +	mem = memblock_alloc(size, PAGE_SIZE);
> +	if (!mem)
> +		return -ENOMEM;
> +
> +	ti = __va(mem);
> +	memset(ti, 0, size);

Can you just use get_zeroed_page()? (struct pvclock_vsyscall_time_info 
is always less than a page, isn't it?).


-boris

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