[xen staging] libxc: use multicall for memory-op on Linux (and Solaris)

[patchbot@xxxxxxx]

commit 6f02d1ea4a109a32f346a5d1de63a42b291c354c
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jun 24 16:39:26 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jun 24 16:39:26 2021 +0200

    libxc: use multicall for memory-op on Linux (and Solaris)
    
    Some sub-functions, XENMEM_maximum_gpfn and XENMEM_maximum_ram_page in
    particular, can return values requiring more than 31 bits to represent.
    Hence we cannot issue the hypercall directly when the return value of
    ioctl() is used to propagate this value. This is the case for Linux
    and Solaris (and hence needs changing), while the BSDs avoid using the
    return value for dual purposes altogether, and MiniOS already wraps all
    hypercalls in a multicall.
    
    Suggested-by: Jürgen Gro� <jgross@xxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/libs/ctrl/xc_private.c | 43 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

diff --git a/tools/libs/ctrl/xc_private.c b/tools/libs/ctrl/xc_private.c
index d94f846686..c0422662f0 100644
--- a/tools/libs/ctrl/xc_private.c
+++ b/tools/libs/ctrl/xc_private.c
@@ -337,8 +337,47 @@ long do_memory_op(xc_interface *xch, int cmd, void *arg, 
size_t len)
         goto out1;
     }
 
-    ret = xencall2(xch->xcall, __HYPERVISOR_memory_op,
-                   cmd, HYPERCALL_BUFFER_AS_ARG(arg));
+#if defined(__linux__) || defined(__sun__)
+    /*
+     * Some sub-ops return values which don't fit in "int". On platforms
+     * without a specific hypercall return value field in the privcmd
+     * interface structure, issue the request as a single-element multicall,
+     * to be able to capture the full return value.
+     */
+    if ( sizeof(long) > sizeof(int) )
+    {
+        multicall_entry_t multicall = {
+            .op = __HYPERVISOR_memory_op,
+            .args[0] = cmd,
+            .args[1] = HYPERCALL_BUFFER_AS_ARG(arg),
+        }, *call = &multicall;
+        DECLARE_HYPERCALL_BOUNCE(call, sizeof(*call),
+                                 XC_HYPERCALL_BUFFER_BOUNCE_BOTH);
+
+        if ( xc_hypercall_bounce_pre(xch, call) )
+        {
+            PERROR("Could not bounce buffer for memory_op hypercall");
+            goto out1;
+        }
+
+        ret = do_multicall_op(xch, HYPERCALL_BUFFER(call), 1);
+
+        xc_hypercall_bounce_post(xch, call);
+
+        if ( !ret )
+        {
+            ret = multicall.result;
+            if ( multicall.result > ~0xfffUL )
+            {
+                errno = -ret;
+                ret = -1;
+            }
+        }
+    }
+    else
+#endif
+        ret = xencall2L(xch->xcall, __HYPERVISOR_memory_op,
+                        cmd, HYPERCALL_BUFFER_AS_ARG(arg));
 
     xc_hypercall_bounce_post(xch, arg);
  out1:
--
generated by git-patchbot for /home/xen/git/xen.git#staging