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Message-ID: <alpine.DEB.2.02.1601191210250.9400@kaball.uk.xensource.com>
Date: Tue, 19 Jan 2016 12:14:32 +0000
From: Stefano Stabellini <stefano.stabellini@...citrix.com>
To: Shannon Zhao <zhaoshenglong@...wei.com>
CC: Stefano Stabellini <stefano.stabellini@...citrix.com>,
<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 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@...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.
> >
> 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.
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