x86/hvm: Fix altp2m_op hypercall continuations

c/s 9383de210 "x86/altp2m: support for setting restrictions for an array of
pages" introduced this logic, but do_hvm_op() was already capable of handling
-ERESTART correctly.

More problematic however is a continuation from compat_altp2m_op().  The arg
written back into register state points into the hypercall XLAT area, not at
the original parameter passed by the guest.  It may be truncated by the
vmentry, but definitely won't be correct on the next invocation.

Delete the hypercall_create_continuation() call, and return -ERESTART, which
will cause the compat case to start working correctly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 30411d7cecc797abdaccb4043ddd2cef00a9ac5a..ed1ff9c87f995a2a149a3174559977dd047dbc81 100644 (file)
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4697,12 +4697,10 @@ static int do_altp2m_op(
         if ( rc > 0 )
         {
             a.u.set_mem_access_multi.opaque = rc;
+            rc = -ERESTART;
             if ( __copy_field_to_guest(guest_handle_cast(arg, xen_hvm_altp2m_op_t),
                                        &a, u.set_mem_access_multi.opaque) )
                 rc = -EFAULT;
-            else
-                rc = hypercall_create_continuation(__HYPERVISOR_hvm_op, "lh",
-                                                   HVMOP_altp2m, arg);
         }
         break;
 
@@ -4821,14 +4819,8 @@ static int compat_altp2m_op(
     switch ( a.cmd )
     {
     case HVMOP_altp2m_set_mem_access_multi:
-        /*
-         * The return code can be positive only if it is the return value
-         * of hypercall_create_continuation. In this case, the opaque value
-         * must be copied back to the guest.
-         */
-        if ( rc > 0 )
+        if ( rc == -ERESTART )
         {
-            ASSERT(rc == __HYPERVISOR_hvm_op);
             a.u.set_mem_access_multi.opaque =
                 nat.altp2m_op->u.set_mem_access_multi.opaque;
             if ( __copy_field_to_guest(guest_handle_cast(arg,