[Qemu-devel] [PATCH QEMU-XEN v8 5/8] xen: Switch uses of xc_map_foreign_{pages, bulk} to use libxenforeignmemory API.

[Ian Campbell <ian.campbell@citrix.com>]

In Xen 4.7 we are refactoring parts libxenctrl into a number of
separate libraries which will provide backward and forward API and ABI
compatiblity.

One such library will be libxenforeignmemory which provides access to
privileged foreign mappings and which will provide an interface
equivalent to xc_map_foreign_{pages,bulk}.

The new xenforeignmemory_map() function behaves like
xc_map_foreign_pages() when the err argument is NULL and like
xc_map_foreign_bulk() when err is non-NULL, which maps into the shim
here onto checking err == NULL and calling the appropriate old
function.

Note that xenforeignmemory_map() takes the number of pages before the
arrays themselves, in order to support potentially future use of
variable-length-arrays in the prototype (in the future, when Xen's
baseline toolchain requirements are new enough to ensure VLAs are
supported).

In preparation for adding support for libxenforeignmemory add support
to the <=4.0 and <=4.6 compat code in xen_common.h to allow us to
switch to using the new API. These shims will disappear for versions
of Xen which include libxenforeignmemory.

Since libxenforeignmemory will have its own handle type but for <= 4.6
the functionality is provided by using a libxenctrl handle we
introduce a new global xen_fmem alongside the existing xen_xc. In fact
we make xen_fmem a pointer to the existing xen_xc, which then works
correctly with both <=4.0 (xc handle is an int) and <=4.6 (xc handle
is a pointer). In the latter case xen_fmem is actually a double
indirect pointer, but it all falls out in the wash.

Unlike libxenctrl libxenforeignmemory has an explicit unmap function,
rather than just specifying that munmap should be used, so the unmap
paths are updated to use xenforeignmemory_unmap, which is a shim for
munmap on these versions of xen. The mappings in xen-hvm.c do not
appear to be unmapped (which makes sense for a qemu-dm process)

In fb_disconnect this results in a change from simply mmap over the
existing mapping (with an implicit munmap) to expliclty unmapping with
xenforeignmemory_unmap and then mapping the required anonymous memory
in the same hole. I don't think this is a problem since any other
thread which was racily touching this region would already be running
the risk of hitting the mapping halfway through the call. If this is
thought to be a problem then we could consider adding an extra API to
the libxenforeignmemory interface to replace a foreign mapping with
anonymous shared memory, but I'd prefer not to.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
---
v8: Move two copies of compat xenforeignmemory_{open,unmap} to the
    common location. Guard with version 471 (which will be added in
    the next patch)
v7: Move two copies of compat xenforeignmemory_map to a common location.
    Note that the existing xen_domain_create #ifdef will be covered by
    a CONFIG_XEN_PV_DOMAIN_BUILD in a later patch, and so is not a
    suitable place to put this function.
v6: Handle _pages as well as _bulk, due to changes in the previous
    patches, including the dropping of "xen: Switch uses of
    xc_map_foreign_pages into xc_map_foreign_bulk" which previous preceded
    this patch and the change of "xen: Switch uses of
    xc_map_foreign_range into xc_map_foreign_bulk" into "xen: Switch
    uses of xc_map_foreign_range into xc_map_foreign_pages".

    Handle reordering of arguments to xenforeignmemory_map().

    Dropped Stefano's Reviewed-by due to these changes.

v4: Rebase onto "xen_console: correctly cleanup primary console on
    teardown."

    xenforeignmemory_unmap takes pages not bytes

    Compat wrapper for xenforeignmemory_open instead of ifdef in code.

    Run check patch and fix most issues. I did not fix:

ERROR: do not initialise globals to 0 or NULL
+xenforeignmemory_handle *xen_fmem = NULL;

=> This is consistent with all of the existing declarations.

ERROR: need consistent spacing around '*' (ctx:WxV)
+typedef xc_interface *xenforeignmemory_handle;

=> I think this is a false +ve since this is a pointer "*" not a multiple "*".

reorder args to xenforeignmemory_map
---
 hw/char/xen_console.c        |  8 ++++----
 hw/display/xenfb.c           | 17 +++++++++--------
 hw/xen/xen_backend.c         |  3 ++-
 include/hw/xen/xen_backend.h |  1 +
 include/hw/xen/xen_common.h  | 25 +++++++++++++++++++++++++
 xen-common.c                 |  6 ++++++
 xen-hvm.c                    | 12 ++++++------
 xen-mapcache.c               |  6 +++---
 8 files changed, 56 insertions(+), 22 deletions(-)

diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index 3e8a57b..b92d0c6 100644
--- a/hw/char/xen_console.c
+++ b/hw/char/xen_console.c
@@ -229,9 +229,9 @@ static int con_initialise(struct XenDevice *xendev)
 
     if (!xendev->dev) {
         xen_pfn_t mfn = con->ring_ref;
-        con->sring = xc_map_foreign_pages(xen_xc, con->xendev.dom,
-                                         PROT_READ|PROT_WRITE,
-                                         &mfn, 1);
+        con->sring = xenforeignmemory_map(xen_fmem, con->xendev.dom,
+                                          PROT_READ|PROT_WRITE,
+                                          1, &mfn, NULL);
     } else {
         con->sring = xengnttab_map_grant_ref(xendev->gnttabdev, con->xendev.dom,
                                              con->ring_ref,
@@ -273,7 +273,7 @@ static void con_disconnect(struct XenDevice *xendev)
 
     if (con->sring) {
         if (!xendev->dev) {
-            munmap(con->sring, XC_PAGE_SIZE);
+            xenforeignmemory_unmap(xen_fmem, con->sring, 1);
         } else {
             xengnttab_unmap(xendev->gnttabdev, con->sring, 1);
         }
diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
index bb8f6b3..a42971c 100644
--- a/hw/display/xenfb.c
+++ b/hw/display/xenfb.c
@@ -106,8 +106,8 @@ static int common_bind(struct common *c)
     if (xenstore_read_fe_int(&c->xendev, "event-channel", &c->xendev.remote_port) == -1)
 	return -1;
 
-    c->page = xc_map_foreign_pages(xen_xc, c->xendev.dom,
-                                   PROT_READ | PROT_WRITE, &mfn, 1);
+    c->page = xenforeignmemory_map(xen_fmem, c->xendev.dom,
+                                   PROT_READ | PROT_WRITE, 1, &mfn, NULL);
     if (c->page == NULL)
 	return -1;
 
@@ -122,7 +122,7 @@ static void common_unbind(struct common *c)
 {
     xen_be_unbind_evtchn(&c->xendev);
     if (c->page) {
-	munmap(c->page, XC_PAGE_SIZE);
+        xenforeignmemory_unmap(xen_fmem, c->page, 1);
 	c->page = NULL;
     }
 }
@@ -495,15 +495,15 @@ static int xenfb_map_fb(struct XenFB *xenfb)
     fbmfns = g_malloc0(sizeof(xen_pfn_t) * xenfb->fbpages);
 
     xenfb_copy_mfns(mode, n_fbdirs, pgmfns, pd);
-    map = xc_map_foreign_pages(xen_xc, xenfb->c.xendev.dom,
-			       PROT_READ, pgmfns, n_fbdirs);
+    map = xenforeignmemory_map(xen_fmem, xenfb->c.xendev.dom,
+                               PROT_READ, n_fbdirs, pgmfns, NULL);
     if (map == NULL)
 	goto out;
     xenfb_copy_mfns(mode, xenfb->fbpages, fbmfns, map);
-    munmap(map, n_fbdirs * XC_PAGE_SIZE);
+    xenforeignmemory_unmap(xen_fmem, map, n_fbdirs);
 
-    xenfb->pixels = xc_map_foreign_pages(xen_xc, xenfb->c.xendev.dom,
-            PROT_READ, fbmfns, xenfb->fbpages);
+    xenfb->pixels = xenforeignmemory_map(xen_fmem, xenfb->c.xendev.dom,
+            PROT_READ, xenfb->fbpages, fbmfns, NULL);
     if (xenfb->pixels == NULL)
 	goto out;
 
@@ -912,6 +912,7 @@ static void fb_disconnect(struct XenDevice *xendev)
      *   Replacing the framebuffer with anonymous shared memory
      *   instead.  This releases the guest pages and keeps qemu happy.
      */
+    xenforeignmemory_unmap(xen_fmem, fb->pixels, fb->fbpages);
     fb->pixels = mmap(fb->pixels, fb->fbpages * XC_PAGE_SIZE,
                       PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON,
                       -1, 0);
diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
index 966e34f..caa459c 100644
--- a/hw/xen/xen_backend.c
+++ b/hw/xen/xen_backend.c
@@ -45,6 +45,7 @@
 
 /* public */
 XenXC xen_xc = XC_HANDLER_INITIAL_VALUE;
+xenforeignmemory_handle *xen_fmem = NULL;
 struct xs_handle *xenstore = NULL;
 const char *xen_protocol;
 
@@ -717,7 +718,7 @@ int xen_be_init(void)
 
     qemu_set_fd_handler(xs_fileno(xenstore), xenstore_update, NULL, NULL);
 
-    if (xen_xc == XC_HANDLER_INITIAL_VALUE) {
+    if (xen_xc == XC_HANDLER_INITIAL_VALUE || xen_fmem == NULL) {
         /* Check if xen_init() have been called */
         goto err;
     }
diff --git a/include/hw/xen/xen_backend.h b/include/hw/xen/xen_backend.h
index 8e8857b..e0d52ee 100644
--- a/include/hw/xen/xen_backend.h
+++ b/include/hw/xen/xen_backend.h
@@ -57,6 +57,7 @@ struct XenDevice {
 
 /* variables */
 extern XenXC xen_xc;
+extern xenforeignmemory_handle *xen_fmem;
 extern struct xs_handle *xenstore;
 extern const char *xen_protocol;
 
diff --git a/include/hw/xen/xen_common.h b/include/hw/xen/xen_common.h
index 8f38310..95275b3 100644
--- a/include/hw/xen/xen_common.h
+++ b/include/hw/xen/xen_common.h
@@ -41,6 +41,7 @@ static inline void *xc_map_foreign_bulk(int xc_handle, uint32_t dom, int prot,
 typedef int XenXC;
 typedef int xenevtchn_handle;
 typedef int xengnttab_handle;
+typedef int xenforeignmemory_handle;
 
 #  define XC_INTERFACE_FMT "%i"
 #  define XC_HANDLER_INITIAL_VALUE    -1
@@ -104,6 +105,8 @@ static inline XenXC xen_xc_interface_open(void *logger, void *dombuild_logger,
     return xc_interface_open();
 }
 
+/* See below for xenforeignmemory_* APIs */
+
 static inline int xc_fd(int xen_xc)
 {
     return xen_xc;
@@ -149,6 +152,7 @@ static inline void xs_close(struct xs_handle *xsh)
 #else
 
 typedef xc_interface *XenXC;
+typedef xc_interface *xenforeignmemory_handle;
 typedef xc_evtchn xenevtchn_handle;
 typedef xc_gnttab xengnttab_handle;
 
@@ -178,6 +182,8 @@ static inline XenXC xen_xc_interface_open(void *logger, void *dombuild_logger,
     return xc_interface_open(logger, dombuild_logger, open_flags);
 }
 
+/* See below for xenforeignmemory_* APIs */
+
 /* FIXME There is now way to have the xen fd */
 static inline int xc_fd(xc_interface *xen_xc)
 {
@@ -501,4 +507,23 @@ static inline int xen_domain_create(XenXC xc, uint32_t ssidref,
 }
 #endif
 
+#if CONFIG_XEN_CTRL_INTERFACE_VERSION < 471
+
+#define xenforeignmemory_open(l, f) &xen_xc
+
+static inline void *xenforeignmemory_map(XenXC *h, uint32_t dom,
+                                         int prot, size_t pages,
+                                         const xen_pfn_t arr[/*pages*/],
+                                         int err[/*pages*/])
+{
+    if (err)
+        return xc_map_foreign_bulk(*h, dom, prot, arr, err, pages);
+    else
+        return xc_map_foreign_pages(*h, dom, prot, arr, pages);
+}
+
+#define xenforeignmemory_unmap(h, p, s) munmap(p, s * XC_PAGE_SIZE)
+
+#endif
+
 #endif /* QEMU_HW_XEN_COMMON_H */
diff --git a/xen-common.c b/xen-common.c
index 0dcdbc3..6cd2959 100644
--- a/xen-common.c
+++ b/xen-common.c
@@ -118,6 +118,12 @@ static int xen_init(MachineState *ms)
         xen_be_printf(NULL, 0, "can't open xen interface\n");
         return -1;
     }
+    xen_fmem = xenforeignmemory_open(0, 0);
+    if (xen_fmem == NULL) {
+        xen_be_printf(NULL, 0, "can't open xen fmem interface\n");
+        xc_interface_close(xen_xc);
+        return -1;
+    }
     qemu_add_vm_change_state_handler(xen_change_state_handler, NULL);
 
     global_state_set_optional();
diff --git a/xen-hvm.c b/xen-hvm.c
index 1f729f6..66ee835 100644
--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -1247,9 +1247,9 @@ int xen_hvm_init(PCMachineState *pcms,
     DPRINTF("buffered io page at pfn %lx\n", bufioreq_pfn);
     DPRINTF("buffered io evtchn is %x\n", bufioreq_evtchn);
 
-    state->shared_page = xc_map_foreign_pages(xen_xc, xen_domid,
+    state->shared_page = xenforeignmemory_map(xen_fmem, xen_domid,
                                               PROT_READ|PROT_WRITE,
-                                              &ioreq_pfn, 1);
+                                              1, &ioreq_pfn, NULL);
     if (state->shared_page == NULL) {
         hw_error("map shared IO page returned error %d handle=" XC_INTERFACE_FMT,
                  errno, xen_xc);
@@ -1259,8 +1259,8 @@ int xen_hvm_init(PCMachineState *pcms,
     if (!rc) {
         DPRINTF("shared vmport page at pfn %lx\n", ioreq_pfn);
         state->shared_vmport_page =
-            xc_map_foreign_pages(xen_xc, xen_domid, PROT_READ|PROT_WRITE,
-                                 &ioreq_pfn, 1);
+            xenforeignmemory_map(xen_fmem, xen_domid, PROT_READ|PROT_WRITE,
+                                 1, &ioreq_pfn, NULL);
         if (state->shared_vmport_page == NULL) {
             hw_error("map shared vmport IO page returned error %d handle="
                      XC_INTERFACE_FMT, errno, xen_xc);
@@ -1269,9 +1269,9 @@ int xen_hvm_init(PCMachineState *pcms,
         hw_error("get vmport regs pfn returned error %d, rc=%d", errno, rc);
     }
 
-    state->buffered_io_page = xc_map_foreign_pages(xen_xc, xen_domid,
+    state->buffered_io_page = xenforeignmemory_map(xen_fmem, xen_domid,
                                                    PROT_READ|PROT_WRITE,
-                                                   &bufioreq_pfn, 1);
+                                                   1, &bufioreq_pfn, NULL);
     if (state->buffered_io_page == NULL) {
         hw_error("map buffered IO page returned error %d", errno);
     }
diff --git a/xen-mapcache.c b/xen-mapcache.c
index 97fece2..4a04378 100644
--- a/xen-mapcache.c
+++ b/xen-mapcache.c
@@ -176,10 +176,10 @@ static void xen_remap_bucket(MapCacheEntry *entry,
         pfns[i] = (address_index << (MCACHE_BUCKET_SHIFT-XC_PAGE_SHIFT)) + i;
     }
 
-    vaddr_base = xc_map_foreign_bulk(xen_xc, xen_domid, PROT_READ|PROT_WRITE,
-                                     pfns, err, nb_pfn);
+    vaddr_base = xenforeignmemory_map(xen_fmem, xen_domid, PROT_READ|PROT_WRITE,
+                                      nb_pfn, pfns, err);
     if (vaddr_base == NULL) {
-        perror("xc_map_foreign_bulk");
+        perror("xenforeignmemory_map");
         exit(-1);
     }
 
-- 
2.1.4