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

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Message-ID: <alpine.DEB.2.02.1601181445210.16178@kaball.uk.xensource.com>
Date:	Mon, 18 Jan 2016 14:59:31 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Shannon Zhao <zhaoshenglong@...wei.com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<ard.biesheuvel@...aro.org>, <stefano.stabellini@...rix.com>,
	<david.vrabel@...rix.com>, <mark.rutland@....com>,
	<devicetree@...r.kernel.org>, <linux-efi@...r.kernel.org>,
	<catalin.marinas@....com>, <will.deacon@....com>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xen.org>,
	<julien.grall@...rix.com>, <shannon.zhao@...aro.org>,
	<peter.huangpeng@...wei.com>
Subject: Re: [Xen-devel] [PATCH v2 10/16] ARM: XEN: Move xen_early_init()
 before efi_init()

On Fri, 15 Jan 2016, Shannon Zhao wrote:
> From: Shannon Zhao <shannon.zhao@...aro.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@...aro.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.


> -	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.


>  		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();