[PATCH v4 1/4] xen: XENMEM_exchange should only be used/compiled for arch supporting PV guest

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

XENMEM_exchange can only be used by PV guest but the check is well
hidden in steal_page(). This is because paging_model_external() will
return false only for PV domain.

To make clearer this is PV only, add a check at the beginning of the
implementation. Take the opportunity to compile out the code if
CONFIG_PV is not set.

This change will also help a follow-up patch where the gmfn_mfn() will
be completely removed on arch not supporting the M2P.

Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

---

Jan suggested to #ifdef anything after the check to is_pv_domain().
However, it means to have two block of #ifdef as we can't mix
declaration and code.

I am actually thinking to move the implementation outside of mm.c in
possibly arch/x86 or a pv specific directory under common. Any opinion?

    Changes in v4:
        - Patch added
---
 xen/common/memory.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 714077c1e597..9300104943b0 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -504,6 +504,7 @@ static bool propagate_node(unsigned int xmf, unsigned int 
*memflags)
 
 static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
 {
+#ifdef CONFIG_PV
     struct xen_memory_exchange exch;
     PAGE_LIST_HEAD(in_chunk_list);
     PAGE_LIST_HEAD(out_chunk_list);
@@ -516,6 +517,9 @@ static long 
memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
     struct domain *d;
     struct page_info *page;
 
+    if ( !is_pv_domain(d) )
+        return -EOPNOTSUPP;
+
     if ( copy_from_guest(&exch, arg, 1) )
         return -EFAULT;
 
@@ -797,6 +801,9 @@ static long 
memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
     if ( __copy_field_to_guest(arg, &exch, nr_exchanged) )
         rc = -EFAULT;
     return rc;
+#else /* !CONFIG_PV */
+    return -EOPNOTSUPP;
+#endif
 }
 
 int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
-- 
2.17.1