linux-kernel - Re: [PATCH 07/24] xen/arm: Xen detection and shared

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Message-ID: <alpine.DEB.2.02.1208011641410.4645@kaball.uk.xensource.com>
Date:	Wed, 1 Aug 2012 16:45:40 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Ian Campbell <Ian.Campbell@...rix.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 07/24] xen/arm: Xen detection and shared_info page
 mapping

On Wed, 1 Aug 2012, Konrad Rzeszutek Wilk wrote:
> On Thu, Jul 26, 2012 at 04:33:49PM +0100, Stefano Stabellini wrote:
> > Check for a "/xen" node in the device tree, if it is present set
> > xen_domain_type to XEN_HVM_DOMAIN and continue initialization.
> > 
> > Map the real shared info page using XENMEM_add_to_physmap with
> > XENMAPSPACE_shared_info.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > ---
> >  arch/arm/xen/enlighten.c |   56 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 files changed, 56 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > index d27c2a6..8c923af 100644
> > --- a/arch/arm/xen/enlighten.c
> > +++ b/arch/arm/xen/enlighten.c
> > @@ -5,6 +5,9 @@
> >  #include <asm/xen/hypervisor.h>
> >  #include <asm/xen/hypercall.h>
> >  #include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/of_irq.h>
> > +#include <linux/of_address.h>
> >  
> >  struct start_info _xen_start_info;
> >  struct start_info *xen_start_info = &_xen_start_info;
> > @@ -33,3 +36,56 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
> >  	return -ENOSYS;
> >  }
> >  EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
> > +
> > +/*
> > + * == Xen Device Tree format ==
> > + * - /xen node;
> > + * - compatible "arm,xen";
> > + * - one interrupt for Xen event notifications;
> > + * - one memory region to map the grant_table.
> > + */
> > +static int __init xen_guest_init(void)
> > +{
> > +	int cpu;
> > +	struct xen_add_to_physmap xatp;
> > +	static struct shared_info *shared_info_page = 0;
> > +	struct device_node *node;
> > +
> > +	node = of_find_compatible_node(NULL, NULL, "arm,xen");
> > +	if (!node) {
> > +		pr_info("No Xen support\n");
> 
> I don't think the pr_info is appropiate here?

Yes, you are right. In fact I had already turned it into a pr_debug.

> > +		return 0;
> 
> Should this be -ENODEV?

Considering that xen_guest_init is called by a core_initcall, I didn't
want to return an error just because Xen is not present on the platform.


> > +	}
> > +	xen_domain_type = XEN_HVM_DOMAIN;
> > +
> > +	if (!shared_info_page)
> > +		shared_info_page = (struct shared_info *)
> > +			get_zeroed_page(GFP_KERNEL);
> > +	if (!shared_info_page) {
> > +		pr_err("not enough memory");
> 
> \n

OK

> > +		return -ENOMEM;
> > +	}
> > +	xatp.domid = DOMID_SELF;
> > +	xatp.idx = 0;
> > +	xatp.space = XENMAPSPACE_shared_info;
> > +	xatp.gpfn = __pa(shared_info_page) >> PAGE_SHIFT;
> > +	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
> > +		BUG();
> > +
> > +	HYPERVISOR_shared_info = (struct shared_info *)shared_info_page;
> > +
> > +	/* xen_vcpu is a pointer to the vcpu_info struct in the shared_info
> > +	 * page, we use it in the event channel upcall and in some pvclock
> > +	 * related functions. We don't need the vcpu_info placement
> > +	 * optimizations because we don't use any pv_mmu or pv_irq op on
> > +	 * HVM.
> > +	 * When xen_hvm_init_shared_info is run at boot time only vcpu 0 is
> > +	 * online but xen_hvm_init_shared_info is run at resume time too and
> > +	 * in that case multiple vcpus might be online. */
> > +	for_each_online_cpu(cpu) {
> > +		per_cpu(xen_vcpu, cpu) =
> > +			&HYPERVISOR_shared_info->vcpu_info[cpu];
> > +	}
> > +	return 0;
> 
> This above looks stringly similar to the x86 one. Could it be
> abstracted away to share the same code? Or is that something that
> ought to be done later on when there is more meat on the bone?

Actually I had to remove these three lines because on ARM we are going
to have just one vcpu_info struct in the shared_info page and then rely
on VCPUOP_register_vcpu_info.
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