Re: [Xen-devel] [PATCH v2 10/16] ARM: XEN: Move xen_early_init() before efi_init()

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Tue, 19 Jan 2016, Shannon Zhao wrote:
> On 2016/1/18 22:59, Stefano Stabellini wrote:
> > On Fri, 15 Jan 2016, Shannon Zhao wrote:
> >> From: Shannon Zhao <shannon.zhao@linaro.org>
> >>
> >> Move xen_early_init() before efi_init(), then when calling efi_init()
> >> could initialize Xen specific UEFI.
> >>
> >> Check if it runs on Xen hypervisor through the flat dts.
> >>
> >> Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
> >> ---
> >>  arch/arm/xen/enlighten.c  | 56 ++++++++++++++++++++++++++++++++++-------------
> >>  arch/arm64/kernel/setup.c |  2 +-
> >>  2 files changed, 42 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> >> index 4e78c49..5d0fe68 100644
> >> --- a/arch/arm/xen/enlighten.c
> >> +++ b/arch/arm/xen/enlighten.c
> >> @@ -19,6 +19,7 @@
> >>  #include <linux/irqreturn.h>
> >>  #include <linux/module.h>
> >>  #include <linux/of.h>
> >> +#include <linux/of_fdt.h>
> >>  #include <linux/of_irq.h>
> >>  #include <linux/of_address.h>
> >>  #include <linux/cpuidle.h>
> >> @@ -52,8 +53,6 @@ struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
> >>  
> >>  static __read_mostly unsigned int xen_events_irq;
> >>  
> >> -static __initdata struct device_node *xen_node;
> >> -
> >>  int xen_remap_domain_gfn_array(struct vm_area_struct *vma,
> >>  			       unsigned long addr,
> >>  			       xen_pfn_t *gfn, int nr,
> >> @@ -222,6 +221,33 @@ static irqreturn_t xen_arm_callback(int irq, void *arg)
> >>  	return IRQ_HANDLED;
> >>  }
> >>  
> >> +static __initdata struct {
> >> +	const char *compat;
> >> +	const char *prefix;
> >> +	const char *version;
> >> +	bool found;
> >> +} xen_node = {"xen,xen", "xen,xen-", NULL, false};
> >> +
> >> +static int __init fdt_find_xen_node(unsigned long node, const char *uname,
> >> +				    int depth, void *data)
> >> +{
> >> +	const void *s = NULL;
> >> +	int len;
> >> +
> >> +	if (depth != 1 || strcmp(uname, "hypervisor") != 0)
> >> +		return 0;
> >> +
> >> +	if (of_flat_dt_is_compatible(node, xen_node.compat))
> >> +		xen_node.found = true;
> >> +
> >> +	s = of_get_flat_dt_prop(node, "compatible", &len);
> >> +	if (strlen(xen_node.prefix) + 3  < len &&
> >> +	    !strncmp(xen_node.prefix, s, strlen(xen_node.prefix)))
> >> +		xen_node.version = s + strlen(xen_node.prefix);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >>  /*
> >>   * see Documentation/devicetree/bindings/arm/xen.txt for the
> >>   * documentation of the Xen Device Tree format.
> >> @@ -229,26 +255,18 @@ static irqreturn_t xen_arm_callback(int irq, void *arg)
> >>  #define GRANT_TABLE_PHYSADDR 0
> >>  void __init xen_early_init(void)
> >>  {
> >> -	int len;
> >> -	const char *s = NULL;
> >> -	const char *version = NULL;
> >> -	const char *xen_prefix = "xen,xen-";
> >> -
> >> -	xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
> >> -	if (!xen_node) {
> >> +	of_scan_flat_dt(fdt_find_xen_node, NULL);
> >> +	if (!xen_node.found) {
> >>  		pr_debug("No Xen support\n");
> >>  		return;
> >>  	}
> >> -	s = of_get_property(xen_node, "compatible", &len);
> >> -	if (strlen(xen_prefix) + 3  < len &&
> >> -			!strncmp(xen_prefix, s, strlen(xen_prefix)))
> >> -		version = s + strlen(xen_prefix);
> >> -	if (version == NULL) {
> >> +
> >> +	if (xen_node.version == NULL) {
> >>  		pr_debug("Xen version not found\n");
> >>  		return;
> >>  	}
> > 
> > This is going to access data within the fdt, after it has been
> > unflattened (by the unflatten_device_tree call). Is that allowed?
> > 
> > If that's not allowed, then you could copy the version string to
> > xen_node.version, rather than just copying the pointer. Otherwise you
> > could move the version check entirely within fdt_find_xen_node and
> > remove the version field from xen_node.
> > 
> A little confused. Since here we move xen_early_init before efi_init and
> before unflatten_device_tree as well, at this moment in xen_early_init
> the fdt is flattened. The xen_node.version is only set in
> fdt_find_xen_node and accessed in xen_early_init.

You are right, sorry, I must have been confused. It might be good to
rename the xen_node variable that this patch introduced in xen_guest_init.



> >> -	pr_info("Xen %s support found\n", version);
> >> +	pr_info("Xen %s support found\n", xen_node.version);
> >>  
> >>  	xen_domain_type = XEN_HVM_DOMAIN;
> >>  
> >> @@ -296,6 +314,14 @@ static int __init xen_guest_init(void)
> >>  		}
> >>  #endif
> >>  	} else {
> >> +		struct device_node *xen_node;
> >> +
> >> +		xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
> >> +		if (!xen_node) {
> >> +			pr_debug("No Xen support\n");
> >> +			return -ENODEV;
> >> +		}
> > 
> > It makes sense to move this into a DT specific init function called from
> > xen_guest_init. Also, given that at this point we know that a Xen node
> > should be present, it makes sense to return EFAULT on error, instead of
> > ENODEV. The error message could be changed to something like: "Xen
> > support was detected before, but it has disappeared" and should be
> > pr_err.
> > 
> OK, thanks.