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

[Shannon Zhao]

On 2016/1/18 22:59, Stefano Stabellini wrote:
> On Fri, 15 Jan 2016, Shannon Zhao wrote:
>> From: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
>>
>> 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@xxxxxxxxxx>
>> ---
>>  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.

> 
>> -	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.
> 
>>  		xen_events_irq = irq_of_parse_and_map(xen_node, 0);
>>  	}
>>  
>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>> index 8119479..a4a2878 100644
>> --- a/arch/arm64/kernel/setup.c
>> +++ b/arch/arm64/kernel/setup.c
>> @@ -313,6 +313,7 @@ void __init setup_arch(char **cmdline_p)
>>  	 */
>>  	local_async_enable();
>>  
>> +	xen_early_init();
>>  	efi_init();
>>  	arm64_memblock_init();
>>  
>> @@ -334,7 +335,6 @@ void __init setup_arch(char **cmdline_p)
>>  	} else {
>>  		psci_acpi_init();
>>  	}
>> -	xen_early_init();
>>  
>>  	cpu_read_bootcpu_ops();
>>  	smp_init_cpus();
> 
> .
> 

-- 
Shannon