6 files changed, 79 insertions, 1 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 000d4199b03e..31e2d5bf3e38 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -982,6 +982,9 @@ ENTRY(xen_hypervisor_callback)
 ENTRY(xen_do_upcall)
 1:      mov %esp, %eax
         call xen_evtchn_do_upcall
+#ifndef CONFIG_PREEMPT
+        call xen_maybe_preempt_hcall
+#endif
         jmp  ret_from_intr
         CFI_ENDPROC
 ENDPROC(xen_hypervisor_callback)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index db13655c3a2a..10074ad9ebf8 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1208,6 +1208,9 @@ ENTRY(xen_do_hypervisor_callback)   # do_hypervisor_callback(struct *pt_regs)
         popq %rsp
         CFI_DEF_CFA_REGISTER rsp
         decl PER_CPU_VAR(irq_count)
+#ifndef CONFIG_PREEMPT
+        call xen_maybe_preempt_hcall
+#endif
         jmp  error_exit
         CFI_ENDPROC
 END(xen_do_hypervisor_callback)
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 2140398a2a8c..2ccd3592d41f 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -2,7 +2,7 @@ ifeq ($(filter y, $(CONFIG_ARM) $(CONFIG_ARM64)),)
 obj-$(CONFIG_HOTPLUG_CPU)               += cpu_hotplug.o
 endif
 obj-$(CONFIG_X86)                       += fallback.o
-obj-y   += grant-table.o features.o balloon.o manage.o
+obj-y   += grant-table.o features.o balloon.o manage.o preempt.o
 obj-y   += events/
 obj-y   += xenbus/
 
diff --git a/drivers/xen/preempt.c b/drivers/xen/preempt.c
new file mode 100644
index 000000000000..a1800c150839
--- /dev/null
+++ b/drivers/xen/preempt.c
@@ -0,0 +1,44 @@
+/*
+ * Preemptible hypercalls
+ *
+ * Copyright (C) 2014 Citrix Systems R&D ltd.
+ *
+ * This source code is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ */
+
+#include <linux/sched.h>
+#include <xen/xen-ops.h>
+
+#ifndef CONFIG_PREEMPT
+
+/*
+ * Some hypercalls issued by the toolstack can take many 10s of
+ * seconds. Allow tasks running hypercalls via the privcmd driver to
+ * be voluntarily preempted even if full kernel preemption is
+ * disabled.
+ *
+ * Such preemptible hypercalls are bracketed by
+ * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
+ * calls.
+ */
+
+DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
+EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
+
+asmlinkage __visible void xen_maybe_preempt_hcall(void)
+{
+        if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
+                     && should_resched())) {
+                /*
+                 * Clear flag as we may be rescheduled on a different
+                 * cpu.
+                 */
+                __this_cpu_write(xen_in_preemptible_hcall, false);
+                _cond_resched();
+                __this_cpu_write(xen_in_preemptible_hcall, true);
+        }
+}
+#endif /* CONFIG_PREEMPT */
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 569a13b9e856..59ac71c4a043 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -56,10 +56,12 @@ static long privcmd_ioctl_hypercall(void __user *udata)
         if (copy_from_user(&hypercall, udata, sizeof(hypercall)))
                 return -EFAULT;
 
+        xen_preemptible_hcall_begin();
         ret = privcmd_call(hypercall.op,
                            hypercall.arg[0], hypercall.arg[1],
                            hypercall.arg[2], hypercall.arg[3],
                            hypercall.arg[4]);
+        xen_preemptible_hcall_end();
 
         return ret;
 }
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 7491ee5d8164..83338210ee04 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -46,4 +46,30 @@ static inline efi_system_table_t __init *xen_efi_probe(void)
 }
 #endif
 
+#ifdef CONFIG_PREEMPT
+
+static inline void xen_preemptible_hcall_begin(void)
+{
+}
+
+static inline void xen_preemptible_hcall_end(void)
+{
+}
+
+#else
+
+DECLARE_PER_CPU(bool, xen_in_preemptible_hcall);
+
+static inline void xen_preemptible_hcall_begin(void)
+{
+        __this_cpu_write(xen_in_preemptible_hcall, true);
+}
+
+static inline void xen_preemptible_hcall_end(void)
+{
+        __this_cpu_write(xen_in_preemptible_hcall, false);
+}
+
+#endif /* CONFIG_PREEMPT */
+
 #endif /* INCLUDE_XEN_OPS_H */