linux-kernel - Re: [PATCH 12/24] xen/arm: Introduce xen_guest

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Message-ID: <1343382151.6812.124.camel@zakaz.uk.xensource.com>
Date:	Fri, 27 Jul 2012 10:42:31 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"Tim (Xen.org)" <tim@....org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"arnd@...db.de" <arnd@...db.de>
Subject: Re: [PATCH 12/24] xen/arm: Introduce xen_guest_init

On Thu, 2012-07-26 at 16:33 +0100, Stefano Stabellini wrote:
> We used to rely on a core_initcall to initialize Xen on ARM, however
> core_initcalls are actually called after early consoles are initialized.
> That means that hvc_xen.c is going to be initialized before Xen.
> 
> Given the lack of a better alternative, just call a new Xen
> initialization function (xen_guest_init) from xen_cons_init.

Can't we just arrange for this to be called super early on from
setup_arch? That's got to be better than calling it from some random
function which happens to get called early enough.

I presume that KVM is going to want some similarly early init hooks etc
and therefore ARM could benefit from the same sort of infrastructure as
is in arch/x86/include/asm/hypervisor.h?


> 
> xen_guest_init has to be arch independent, so write both an ARM and an
> x86 implementation. The x86 implementation is currently empty because we
> can be sure that xen_hvm_guest_init is called early enough.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
>  arch/arm/xen/enlighten.c  |    7 ++++++-
>  arch/x86/xen/enlighten.c  |    8 ++++++++
>  drivers/tty/hvc/hvc_xen.c |    7 ++++++-
>  include/xen/xen.h         |    2 ++
>  4 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 8c923af..dc68074 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -44,7 +44,7 @@ EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
>   * - one interrupt for Xen event notifications;
>   * - one memory region to map the grant_table.
>   */
> -static int __init xen_guest_init(void)
> +int __init xen_guest_init(void)
>  {
>  	int cpu;
>  	struct xen_add_to_physmap xatp;
> @@ -58,6 +58,10 @@ static int __init xen_guest_init(void)
>  	}
>  	xen_domain_type = XEN_HVM_DOMAIN;
>  
> +	/* already setup */
> +	if (shared_info_page != 0 && HYPERVISOR_shared_info == shared_info_page)
> +		return 0;
> +
>  	if (!shared_info_page)
>  		shared_info_page = (struct shared_info *)
>  			get_zeroed_page(GFP_KERNEL);
> @@ -88,4 +92,5 @@ static int __init xen_guest_init(void)
>  	}
>  	return 0;
>  }
> +EXPORT_SYMBOL_GPL(xen_guest_init);
>  core_initcall(xen_guest_init);
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index ff962d4..6131d43 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1567,4 +1567,12 @@ const struct hypervisor_x86 x86_hyper_xen_hvm __refconst = {
>  	.init_platform		= xen_hvm_guest_init,
>  };
>  EXPORT_SYMBOL(x86_hyper_xen_hvm);
> +
> +int __init xen_guest_init(void)
> +{
> +	/* do nothing: rely on x86_hyper_xen_hvm for the initialization */
> +	return 0;
> +	
> +}
> +EXPORT_SYMBOL_GPL(xen_guest_init);
>  #endif
> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> index dc07f56..3c04fb8 100644
> --- a/drivers/tty/hvc/hvc_xen.c
> +++ b/drivers/tty/hvc/hvc_xen.c
> @@ -577,6 +577,12 @@ static void __exit xen_hvc_fini(void)
>  static int xen_cons_init(void)
>  {
>  	const struct hv_ops *ops;
> +	int r;
> +
> +	/* retrieve xen infos  */
> +	r = xen_guest_init();
> +	if (r < 0)
> +		return r;
>  
>  	if (!xen_domain())
>  		return 0;
> @@ -584,7 +590,6 @@ static int xen_cons_init(void)
>  	if (xen_initial_domain())
>  		ops = &dom0_hvc_ops;
>  	else {
> -		int r;
>  		ops = &domU_hvc_ops;
>  
>  		if (xen_hvm_domain())
> diff --git a/include/xen/xen.h b/include/xen/xen.h
> index 2c0d3a5..792a4d2 100644
> --- a/include/xen/xen.h
> +++ b/include/xen/xen.h
> @@ -9,8 +9,10 @@ enum xen_domain_type {
>  
>  #ifdef CONFIG_XEN
>  extern enum xen_domain_type xen_domain_type;
> +int xen_guest_init(void);
>  #else
>  #define xen_domain_type		XEN_NATIVE
> +static inline int xen_guest_init(void) { return 0; }
>  #endif
>  
>  #define xen_domain()		(xen_domain_type != XEN_NATIVE)


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