linux-kernel - Re: [Xen-devel] [PATCH 3/4] xen/hvc: Check HVM_PARAM_CONSOLE

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Date:	Fri, 25 May 2012 10:13:47 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 3/4] xen/hvc: Check HVM_PARAM_CONSOLE_[EVTCHN|PFN]
 for correctness.

On Thu, 24 May 2012, Konrad Rzeszutek Wilk wrote:
> > I think that we should add a comment stating that even though mfn = 0
> > and evtchn = 0 are theoretically correct values, in practice they never
> > are and they mean that a legacy toolstack hasn't initialized the pv
> > console correctly.
> 
> Like this?

Yep

> >From 5842f5768599094758931b74190cdf93641a8e35 Mon Sep 17 00:00:00 2001
> From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Date: Wed, 23 May 2012 12:56:59 -0400
> Subject: [PATCH] xen/hvc: Check HVM_PARAM_CONSOLE_[EVTCHN|PFN] for
>  correctness.
> 
> We need to make sure that those parameters are setup to be correct.
> As such the value of 0 is deemed invalid and we find that we
> bail out. The hypervisor sets by default all of them to be zero
> and when the hypercall is done does a simple:
> 
>  a.value = d->arch.hvm_domain.params[a.index];
> 
> Which means that if the Xen toolstack forgot to setup the proper
> HVM_PARAM_CONSOLE_EVTCHN (or the PFN one), we would get the
> default value of 0 and use that.
> 
> CC: stable@...nel.org
> Fixes-Oracle-Bug: 14091238
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

Acked-by: Stefano Stabellini <stefano.stabellini@...citrix.com>

> ---
>  drivers/tty/hvc/hvc_xen.c |   11 ++++++++---
>  1 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> index 3277f0e..944eaeb 100644
> --- a/drivers/tty/hvc/hvc_xen.c
> +++ b/drivers/tty/hvc/hvc_xen.c
> @@ -214,14 +214,19 @@ static int xen_hvm_console_init(void)
>  	/* already configured */
>  	if (info->intf != NULL)
>  		return 0;
> -
> +	/*
> +	 * If the toolstack (or the hypervisor) hasn't set these values, the
> +	 * default value is 0. Even though mfn = 0 and evtchn = 0 are
> +	 * theoretically correct values, in practice they never are and they
> +	 * mean that a legacy toolstack hasn't initialized the pv console correctly.
> +	 */
>  	r = hvm_get_parameter(HVM_PARAM_CONSOLE_EVTCHN, &v);
> -	if (r < 0)
> +	if (r < 0 || v == 0)
>  		goto err;
>  	info->evtchn = v;
>  	v = 0;
>  	r = hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &v);
> -	if (r < 0)
> +	if (r < 0 || v == 0)
>  		goto err;
>  	mfn = v;
>  	info->intf = ioremap(mfn << PAGE_SHIFT, PAGE_SIZE);
> -- 
> 1.7.7.5
> 
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