[Xen-devel] [PATCH v4 4/6] xen: add xen_pin_vcpu() to support calling functions on a dedicated pcpu

[Juergen Gross <jgross@xxxxxxxx>]

Some hardware models (e.g. Dell Studio 1555 laptops) require calls to
the firmware to be issued on cpu 0 only. As Dom0 might have to use
these calls, add xen_pin_vcpu() to achieve this functionality.

In case either the domain doesn't have the privilege to make the
related hypercall or the hypervisor isn't supporting it, issue a
warning once and disable further pinning attempts.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/xen/enlighten.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 880862c..7907bcf8 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1885,6 +1885,45 @@ static void xen_set_cpu_features(struct cpuinfo_x86 *c)
        }
 }
 
+static void xen_pin_vcpu(int cpu)
+{
+       static bool disable_pinning;
+       struct sched_pin_override pin_override;
+       int ret;
+
+       if (disable_pinning)
+               return;
+
+       pin_override.pcpu = cpu;
+       ret = HYPERVISOR_sched_op(SCHEDOP_pin_override, &pin_override);
+       if (cpu < 0)
+               return;
+
+       switch (ret) {
+       case -ENOSYS:
+               pr_warn("The kernel tried to call a function on physical cpu 
%d, but Xen isn't\n"
+                       "supporting this. In case of problems you might 
consider vcpu pinning.\n",
+                       cpu);
+               disable_pinning = true;
+               break;
+       case -EPERM:
+               WARN(1, "Trying to pin vcpu without having privilege to do 
so\n");
+               disable_pinning = true;
+               break;
+       case -EINVAL:
+       case -EBUSY:
+               pr_warn("The kernel tried to call a function on physical cpu 
%d, but this cpu\n"
+                       "seems not to be available. Please check your Xen cpu 
configuration.\n",
+                       cpu);
+               break;
+       case 0:
+               break;
+       default:
+               WARN(1, "rc %d while trying to pin vcpu\n", ret);
+               disable_pinning = true;
+       }
+}
+
 const struct hypervisor_x86 x86_hyper_xen = {
        .name                   = "Xen",
        .detect                 = xen_platform,
@@ -1893,6 +1932,7 @@ const struct hypervisor_x86 x86_hyper_xen = {
 #endif
        .x2apic_available       = xen_x2apic_para_available,
        .set_cpu_features       = xen_set_cpu_features,
+       .pin_vcpu               = xen_pin_vcpu,
 };
 EXPORT_SYMBOL(x86_hyper_xen);
 
-- 
2.6.2


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