[PATCH v5 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.

In a follow-up patch, mfn_to_gfn() will be completely removed for
arch not supporting M2P as it is a call for trouble to use it.
Take the opportunity to compile out the code if CONFIG_PV is not set.

Ideally, we would want to to move the hypercall implementation in
arch/x86/pv/mm.c. But this is incredibly tangled.

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

---

Ideally we would want to move the hypercall implementation in
arch/x86/pv/mm.c. But this is a bit messy. So for now just #ifdef it.

Changes in v5:
    - Removed the #ifdef CONFIG_X86 as they are not necessary anymore
    - Used paging_mode_translate() rather than is_pv_domain()
    - Reword the commit message to explain why the #ifdef rather than
      implementing mfn_to_gfn() using a BUG_ON() or moving the code
      to arch/x86/pv.

Changes in v4:
    - Patch added
---
 xen/common/memory.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index e07bd9a5ea4b..9bc78aae35db 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -522,6 +522,7 @@ 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);
@@ -609,6 +610,13 @@ static long 
memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
         goto fail_early;
     }
 
+    if ( paging_mode_translate(d) )
+    {
+        rc = -EOPNOTSUPP;
+        rcu_unlock_domain(d);
+        goto fail_early;
+    }
+
     rc = xsm_memory_exchange(XSM_TARGET, d);
     if ( rc )
     {
@@ -648,7 +656,6 @@ static long 
memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
 
             for ( k = 0; k < (1UL << exch.in.extent_order); k++ )
             {
-#ifdef CONFIG_X86
                 p2m_type_t p2mt;
 
                 /* Shared pages cannot be exchanged */
@@ -659,14 +666,9 @@ static long 
memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
                     rc = -ENOMEM;
                     goto fail; 
                 }
-#else /* !CONFIG_X86 */
-                mfn = gfn_to_mfn(d, _gfn(gmfn + k));
-#endif
                 if ( unlikely(!mfn_valid(mfn)) )
                 {
-#ifdef CONFIG_X86
                     put_gfn(d, gmfn + k);
-#endif
                     rc = -EINVAL;
                     goto fail;
                 }
@@ -676,16 +678,12 @@ static long 
memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
                 rc = steal_page(d, page, MEMF_no_refcount);
                 if ( unlikely(rc) )
                 {
-#ifdef CONFIG_X86
                     put_gfn(d, gmfn + k);
-#endif
                     goto fail;
                 }
 
                 page_list_add(page, &in_chunk_list);
-#ifdef CONFIG_X86
                 put_gfn(d, gmfn + k);
-#endif
             }
         }
 
@@ -768,8 +766,7 @@ static long 
memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
             guest_physmap_add_page(d, _gfn(gpfn), mfn,
                                    exch.out.extent_order);
 
-            if ( !paging_mode_translate(d) &&
-                 __copy_mfn_to_guest_offset(exch.out.extent_start,
+            if ( __copy_mfn_to_guest_offset(exch.out.extent_start,
                                             (i << out_chunk_order) + j,
                                             mfn) )
                 rc = -EFAULT;
@@ -815,6 +812,9 @@ 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