Re: [PATCHEs]: support more than 32 VCPUs in guests

[Mukesh Rathor <mukesh.rathor@oracle.com>]

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On Mon, 14 Jun 2010 10:37:30 +0100
Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> On 06/10/2010 03:13 AM, Mukesh Rathor wrote:
> > Well, BUG_ON is only triggered if booting more than 32 VCPUs on a
> > *very old* xen (pre xen 3.1.0). 
> >
> > Looking at code closely, we could just set setup_max_cpus to 32 some
> > where in xen function, perhaps even in xen_vcpu_setup(). That way
> > later in smp_init() it would just be ok. 
> >   
> 
> Yes.
> 
> > One thing tho, the per cpus areas are already setup at that point,
> > so that would need to be cleaned. BTW, I don't understand why 
> > have_vcpu_info_placement is set to 0 in xen_guest_init()? 
> >   
> 
> xen_guest_init is used by the pvhvm path, and hvm domains don't have a
> notion of vcpu info placement.
> 
> > What minimum version of xen is required to run pvops kernel?
> >   
> 
> In theory it should be back-compatible for all Xen 3, but in practice
> it tweaks lots of bugs in older Xens (particularly 32-on-64).  I
> don't know that anyone has definitively established an earliest
> version.  I implemented vcpu info placement for use in pvops kernels,
> but it was never my intention that it be an absolute requirement.
> 
>     J

Ok, attached  patch without BUG_ON. Please feel free to modify
to your liking also.

Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>


thanks,
Mukesh

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diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 615897c..5dc7667 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -111,40 +111,46 @@ static int have_vcpu_info_placement = 1;
 
 static void xen_vcpu_setup(int cpu)
 {
-	struct vcpu_register_vcpu_info info;
-	int err;
-	struct vcpu_info *vcpup;
-
-	BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
-	per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
-
-	if (!have_vcpu_info_placement)
-		return;		/* already tested, not available */
-
-	vcpup = &per_cpu(xen_vcpu_info, cpu);
-
-	info.mfn = arbitrary_virt_to_mfn(vcpup);
-	info.offset = offset_in_page(vcpup);
-
-	printk(KERN_DEBUG "trying to map vcpu_info %d at %p, mfn %llx, offset %d\n",
-	       cpu, vcpup, info.mfn, info.offset);
-
-	/* Check to see if the hypervisor will put the vcpu_info
-	   structure where we want it, which allows direct access via
-	   a percpu-variable. */
-	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);
-
-	if (err) {
-		printk(KERN_DEBUG "register_vcpu_info failed: err=%d\n", err);
-		have_vcpu_info_placement = 0;
-	} else {
-		/* This cpu is using the registered vcpu info, even if
-		   later ones fail to. */
-		per_cpu(xen_vcpu, cpu) = vcpup;
-
-		printk(KERN_DEBUG "cpu %d using vcpu_info at %p\n",
-		       cpu, vcpup);
-	}
+        struct vcpu_register_vcpu_info info;
+        int err;
+        struct vcpu_info *vcpup;
+
+        BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
+
+        if (cpu < MAX_VIRT_CPUS)
+                per_cpu(xen_vcpu,cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
+
+        if (!have_vcpu_info_placement) {
+                if (cpu >= MAX_VIRT_CPUS && setup_max_cpus > MAX_VIRT_CPUS)
+                        setup_max_cpus = MAX_VIRT_CPUS;
+                return;
+        }
+
+        vcpup = &per_cpu(xen_vcpu_info, cpu);
+        info.mfn = arbitrary_virt_to_mfn(vcpup);
+        info.offset = offset_in_page(vcpup);
+
+        printk(KERN_DEBUG "trying to map vcpu_info %d at %p, mfn %llx, offset %d\n",
+               cpu, vcpup, info.mfn, info.offset);
+
+        /* Check to see if the hypervisor will put the vcpu_info
+           structure where we want it, which allows direct access via
+           a percpu-variable. */
+        err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);
+
+        if (err) {
+                printk(KERN_DEBUG "register_vcpu_info failed: err=%d\n", err);
+                have_vcpu_info_placement = 0;
+                if (setup_max_cpus > MAX_VIRT_CPUS)
+                        setup_max_cpus = MAX_VIRT_CPUS;
+        } else {
+                /* This cpu is using the registered vcpu info, even if
+                   later ones fail to. */
+                per_cpu(xen_vcpu, cpu) = vcpup;
+
+                printk(KERN_DEBUG "cpu %d using vcpu_info at %p\n",
+                       cpu, vcpup);
+        }
 }
 
 /*

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