[PATCH for-4.15] xen/mm: Fix build when CONFIG_HVM=n and CONFIG_COVERAGE=y

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

Xen is heavily relying on the DCE stage to remove unused code so the
linker doesn't throw an error because a function is not implemented
yet we defined a prototype for it.

On some GCC version (such as 9.4 provided by Debian sid), the compiler
will DCE stage will not managed to figure that out for
xenmem_add_to_physmap_batch():

ld: ld: prelink.o: in function `xenmem_add_to_physmap_batch':
/xen/xen/common/memory.c:942: undefined reference to `xenmem_add_to_physmap_one'
/xen/xen/common/memory.c:942:(.text+0x22145): relocation truncated
to fit: R_X86_64_PLT32 against undefined symbol `xenmem_add_to_physmap_one'
prelink-efi.o: in function `xenmem_add_to_physmap_batch':
/xen/xen/common/memory.c:942: undefined reference to `xenmem_add_to_physmap_one'
make[2]: *** [Makefile:215: /root/xen/xen/xen.efi] Error 1
make[2]: *** Waiting for unfinished jobs....
ld: /xen/xen/.xen-syms.0: hidden symbol `xenmem_add_to_physmap_one' isn't 
defined
ld: final link failed: bad value

It is not entirely clear why the compiler DCE is not detecting the
unused code. However, moving the permission check from do_memory_op()
to xenmem_add_to_physmap_batch() does the trick.

Note that this required to move the implementation of
xapt_permision_check() earlier on so it can be called in
xemem_add_to_physmap_batch().

No functional change intended.

Fixes: d4f699a0df6c ("x86/mm: p2m_add_foreign() is HVM-only")
Reported-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

---

This also resolves a randconfig issue on the gitlab CI.

The gitlab CI is used to provide basic testing on a per-series basis. So
I would like to request this patch to be merged in Xen 4.15 in order to
reduce the number of failure not related to the series tested.

Note that there are a few more randconfig issues that needs to be
addressed.
---
 xen/common/memory.c | 44 +++++++++++++++++++++-----------------------
 1 file changed, 21 insertions(+), 23 deletions(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 01cab7e4930e..b047a93a703a 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -898,11 +898,32 @@ int xenmem_add_to_physmap(struct domain *d, struct 
xen_add_to_physmap *xatp,
     return rc;
 }
 
+static long xatp_permission_check(struct domain *d, unsigned int space)
+{
+    if ( !paging_mode_translate(d) )
+        return -EACCES;
+
+    /*
+     * XENMAPSPACE_dev_mmio mapping is only supported for hardware Domain
+     * to map this kind of space to itself.
+     */
+    if ( (space == XENMAPSPACE_dev_mmio) &&
+         (!is_hardware_domain(d) || (d != current->domain)) )
+        return -EACCES;
+
+    return xsm_add_to_physmap(XSM_TARGET, current->domain, d);
+}
+
 static int xenmem_add_to_physmap_batch(struct domain *d,
                                        struct xen_add_to_physmap_batch *xatpb,
                                        unsigned int extent)
 {
     union add_to_physmap_extra extra = {};
+    int rc;
+
+    rc = xatp_permission_check(d, xatpb->space);
+    if ( rc )
+        return rc;
 
     if ( unlikely(xatpb->size < extent) )
         return -EILSEQ;
@@ -1038,22 +1059,6 @@ static int get_reserved_device_memory(xen_pfn_t start, 
xen_ulong_t nr,
 }
 #endif
 
-static long xatp_permission_check(struct domain *d, unsigned int space)
-{
-    if ( !paging_mode_translate(d) )
-        return -EACCES;
-
-    /*
-     * XENMAPSPACE_dev_mmio mapping is only supported for hardware Domain
-     * to map this kind of space to itself.
-     */
-    if ( (space == XENMAPSPACE_dev_mmio) &&
-         (!is_hardware_domain(d) || (d != current->domain)) )
-        return -EACCES;
-
-    return xsm_add_to_physmap(XSM_TARGET, current->domain, d);
-}
-
 unsigned int ioreq_server_max_frames(const struct domain *d)
 {
     unsigned int nr = 0;
@@ -1442,13 +1447,6 @@ long do_memory_op(unsigned long cmd, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( d == NULL )
             return -ESRCH;
 
-        rc = xatp_permission_check(d, xatpb.space);
-        if ( rc )
-        {
-            rcu_unlock_domain(d);
-            return rc;
-        }
-
         rc = xenmem_add_to_physmap_batch(d, &xatpb, start_extent);
 
         rcu_unlock_domain(d);
-- 
2.17.1