[PATCH] Hypercall continuation cancelation in compat mode for XENMEM_get/set_pod_target.

[Jean Guyader <jean.guyader@eu.citrix.com>]

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If copy_to_guest failed in the compat code after a continuation as been
done in the native code we need to cancel it so we won't reexecute the
hypercall but return from the hypercall with the appropriate error.

Signed-off-by: Jean Guyader <jean.guyader@eu.citrix.com>
---
 xen/arch/x86/domain.c           |   18 ++++++++++++++++++
 xen/arch/x86/x86_64/compat/mm.c |    4 ++++
 xen/include/xen/sched.h         |    1 +
 3 files changed, 23 insertions(+), 0 deletions(-)


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diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 52c7f37..acc3241 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1723,6 +1723,24 @@ void sync_vcpu_execstate(struct vcpu *v)
     __arg;                                                                  \
 })
 
+void hypercall_cancel_continuation(void)
+{
+    struct cpu_user_regs *regs = guest_cpu_user_regs();
+    struct mc_state *mcs = &current->mc_state;
+
+    if ( test_bit(_MCSF_in_multicall, &mcs->flags) )
+    {
+        __clear_bit(_MCSF_call_preempted, &mcs->flags);
+    }
+    else
+    {
+        if ( !is_hvm_vcpu(current) )
+            regs->eip += 2; /* skip re-execute 'syscall' / 'int $xx' */
+        else
+            current->arch.hvm_vcpu.hcall_preempted = 0;
+    }
+}
+
 unsigned long hypercall_create_continuation(
     unsigned int op, const char *format, ...)
 {
diff --git a/xen/arch/x86/x86_64/compat/mm.c b/xen/arch/x86/x86_64/compat/mm.c
index 2c05099..3ef08a5 100644
--- a/xen/arch/x86/x86_64/compat/mm.c
+++ b/xen/arch/x86/x86_64/compat/mm.c
@@ -133,7 +133,11 @@ int compat_arch_memory_op(int op, XEN_GUEST_HANDLE(void) arg)
         XLAT_pod_target(&cmp, nat);
 
         if ( copy_to_guest(arg, &cmp, 1) )
+        {
+            if ( rc == __HYPERVISOR_memory_op )
+                hypercall_cancel_continuation();
             rc = -EFAULT;
+        }
 
         break;
     }
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 3ba5495..80d5c4b 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -554,6 +554,7 @@ extern void (*dead_idle) (void);
  */
 unsigned long hypercall_create_continuation(
     unsigned int op, const char *format, ...);
+void hypercall_cancel_continuation(void);
 
 #define hypercall_preempt_check() (unlikely(    \
         softirq_pending(smp_processor_id()) |   \

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