Re: [Xen-devel] [PATCH v4 07/24] xen/arm: Xen detection and shared_info page mapping

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 14 Sep 2012, Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 14, 2012 at 12:13:09PM +0100, Stefano Stabellini wrote:
> > Check for a node in the device tree compatible with "xen,xen", 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.
> > 
> > Changes in v4:
> > 
> > - simpler parsing of Xen version in the compatible DT node.
> > 
> > Changes in v3:
> > 
> > - use the "xen,xen" notation rather than "arm,xen";
> > - add an additional check on the presence of the Xen version.
> > 
> > Changes in v2:
> > 
> > - replace pr_info with pr_debug.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> >  arch/arm/xen/enlighten.c |   61 
> > ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 files changed, 61 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > index c535540..6a0217d 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 +36,61 @@ int xen_remap_domain_mfn_range(struct vm_area_struct 
> > *vma,
> >     return -ENOSYS;
> >  }
> >  EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
> > +
> > +/*
> > + * see Documentation/devicetree/bindings/arm/xen.txt for the
> > + * documentation of the Xen Device Tree format.
> > + */
> > +static int __init xen_guest_init(void)
> > +{
> > +   struct xen_add_to_physmap xatp;
> > +   static struct shared_info *shared_info_page = 0;
> > +   struct device_node *node;
> > +   int len;
> > +   const char *s = NULL;
> > +   const char *version = NULL;
> > +   const char *xen_prefix = "xen,xen-";
> > +
> > +   node = of_find_compatible_node(NULL, NULL, "xen,xen");
> > +   if (!node) {
> > +           pr_debug("No Xen support\n");
> > +           return 0;
> > +   }
> > +   s = of_get_property(node, "compatible", &len);
> > +   if (strlen(xen_prefix) + 3  < len &&
> > +                   !strncmp(xen_prefix, s, strlen(xen_prefix)))
> 
> If we have version '4.3.1' won't this trip us over?

This isn't an issue:

if (8 + 3 < 14 &&
    !strncmp("xen,xen-", "xen,xen-4.3.1", 8)

would return true

and version is set to "4.3.1".


> Or if we only have 'major' and 'minor', then won't '4.11' trip us
> over too?

For the same reason this shouldn't be an issue either:

if (8 + 3 < 13 &&
    !strncmp("xen,xen-", "xen,xen-4.11", 8)

would return true

and version would be set to "4.11".

BTW I have just tried both out of paranoia and it works as expected.


> > +           version = s + strlen(xen_prefix);
> > +   if (version == NULL) {
> > +           pr_debug("Xen version not found\n");
> > +           return 0;
> > +   }
> > +   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");
> > +           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.
> > +    * The shared info contains exactly 1 CPU (the boot CPU). The guest
> > +    * is required to use VCPUOP_register_vcpu_info to place vcpu info
> > +    * for secondary CPUs as they are brought up. */
> > +   per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
> > +   return 0;
> > +}
> > +core_initcall(xen_guest_init);
> > -- 
> > 1.7.2.5
> 

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