tools/libxencall: use hypercall buffer device if available

Instead of using anonymous memory for hypercall buffers which is then
locked into memory, use the hypercall buffer device of the Linux
privcmd driver if available.

This has the advantage of needing just a single mmap() for allocating
the buffer and page migration or compaction can't make the buffer
unaccessible for the hypervisor.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/tools/libs/call/core.c b/tools/libs/call/core.c
index f3a34009da1a004098afa25526f264c2a6c643f2..46ca61529e946194b380b0c1cbbbc602eae2624c 100644 (file)
--- a/tools/libs/call/core.c
+++ b/tools/libs/call/core.c
@@ -19,7 +19,16 @@
 
 static int all_restrict_cb(Xentoolcore__Active_Handle *ah, domid_t domid) {
     xencall_handle *xcall = CONTAINER_OF(ah, *xcall, tc_ah);
-    return xentoolcore__restrict_by_dup2_null(xcall->fd);
+    int rc;
+
+    rc = xentoolcore__restrict_by_dup2_null(xcall->buf_fd);
+    if ( rc )
+        goto out;
+
+    rc = xentoolcore__restrict_by_dup2_null(xcall->fd);
+
+out:
+    return rc;
 }
 
 xencall_handle *xencall_open(xentoollog_logger *logger, unsigned open_flags)
@@ -30,6 +39,7 @@ xencall_handle *xencall_open(xentoollog_logger *logger, unsigned open_flags)
     if (!xcall) return NULL;
 
     xcall->fd = -1;
+    xcall->buf_fd = -1;
     xcall->tc_ah.restrict_callback = all_restrict_cb;
     xentoolcore__register_active_handle(&xcall->tc_ah);
 

diff --git a/tools/libs/call/linux.c b/tools/libs/call/linux.c
index 3f1b691fe77cd80cacd265e7e0ae2f53eda80ded..90c2691486abdcf7dc4db1e33e33cb2a2741fabb 100644 (file)
--- a/tools/libs/call/linux.c
+++ b/tools/libs/call/linux.c
@@ -56,15 +56,28 @@ int osdep_xencall_open(xencall_handle *xcall)
     }
 
     xcall->fd = fd;
+
+    /*
+     * Try the same for the hypercall buffer device.
+     */
+    fd = open("/dev/xen/hypercall", O_RDWR|O_CLOEXEC);
+    if ( fd == -1 && errno != ENOENT )
+    {
+        PERROR("Error on trying to open hypercall buffer device");
+        return -1;
+    }
+    xcall->buf_fd = fd;
+
     return 0;
 }
 
 int osdep_xencall_close(xencall_handle *xcall)
 {
-    int fd = xcall->fd;
-    if (fd == -1)
-        return 0;
-    return close(fd);
+    if ( xcall->buf_fd >= 0 )
+        close(xcall->buf_fd);
+    if ( xcall->fd >= 0 )
+        close(xcall->fd);
+    return 0;
 }
 
 int osdep_hypercall(xencall_handle *xcall, privcmd_hypercall_t *hypercall)
@@ -72,7 +85,22 @@ int osdep_hypercall(xencall_handle *xcall, privcmd_hypercall_t *hypercall)
     return ioctl(xcall->fd, IOCTL_PRIVCMD_HYPERCALL, hypercall);
 }
 
-void *osdep_alloc_pages(xencall_handle *xcall, size_t npages)
+static void *alloc_pages_bufdev(xencall_handle *xcall, size_t npages)
+{
+    void *p;
+
+    p = mmap(NULL, npages * PAGE_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED,
+             xcall->buf_fd, 0);
+    if ( p == MAP_FAILED )
+    {
+        PERROR("alloc_pages: mmap failed");
+        p = NULL;
+    }
+
+    return p;
+}
+
+static void *alloc_pages_nobufdev(xencall_handle *xcall, size_t npages)
 {
     size_t size = npages * PAGE_SIZE;
     void *p;
@@ -116,11 +144,27 @@ out:
     return NULL;
 }
 
+void *osdep_alloc_pages(xencall_handle *xcall, size_t npages)
+{
+    void *p;
+
+    if ( xcall->buf_fd >= 0 )
+        p = alloc_pages_bufdev(xcall, npages);
+    else
+        p = alloc_pages_nobufdev(xcall, npages);
+
+    return p;
+}
+
 void osdep_free_pages(xencall_handle *xcall, void *ptr, size_t npages)
 {
     int saved_errno = errno;
-    /* Recover the VMA flags. Maybe it's not necessary */
-    madvise(ptr, npages * PAGE_SIZE, MADV_DOFORK);
+
+    if ( xcall->buf_fd < 0 )
+    {
+        /* Recover the VMA flags. Maybe it's not necessary */
+        madvise(ptr, npages * PAGE_SIZE, MADV_DOFORK);
+    }
 
     munmap(ptr, npages * PAGE_SIZE);
     /* We MUST propagate the hypercall errno, not unmap call's. */

diff --git a/tools/libs/call/private.h b/tools/libs/call/private.h
index 533f0c4a8b162f406d460b5b477b0e7fb9530249..21f992b37ed999d73fccb4cc2dce1d069fa6f62b 100644 (file)
--- a/tools/libs/call/private.h
+++ b/tools/libs/call/private.h
@@ -20,7 +20,12 @@
 struct xencall_handle {
     xentoollog_logger *logger, *logger_tofree;
     unsigned flags;
-    int fd;
+
+                     /* partially     with /dev/     no /dev/      */
+                     /* initialised   xen/hypercall  xen/hypercall */
+    int fd;          /*    any           >= 0           >= 0       */
+    int buf_fd;      /*    any           >= 0           -1         */
+
     Xentoolcore__Active_Handle tc_ah;
 
     /*