libxl: support unmapping static shared memory areas during domain destruction

Add libxl__sshm_del to unmap static shared memory areas mapped by
libxl__sshm_add during domain creation. The unmapping process is:

* For a owner: decrease the refcount of the sshm region, if the refcount
  reaches 0, cleanup the whole sshm path.

* For a borrower:
  1) unmap the shared pages, and cleanup related xs entries. If the
     system works normally, all the shared pages will be unmapped, so there
     won't be page leaks. In case of errors, the unmapping process will go
     on and unmap all the other pages that can be unmapped, so the other
     pages won't be leaked, either.
  2) Decrease the refcount of the sshm region, if the refcount reaches
     0, cleanup the whole sshm path.

This is for the proposal "Allow setting up shared memory areas between VMs
from xl config file" (see [1]).

[1] https://lists.xen.org/archives/html/xen-devel/2017-08/msg03242.html

Signed-off-by: Zhongze Liu <blackskygg@gmail.com>
Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Julien Grall <julien.grall@arm.com>
Cc: xen-devel@lists.xen.org

diff --git a/tools/libxl/libxl_domain.c b/tools/libxl/libxl_domain.c
index 5714501778585e2139dc4b5d4234d01dae258205..a72c4e94842f93bdcf6c2a169f3c5cf2f68f5d6d 100644 (file)
--- a/tools/libxl/libxl_domain.c
+++ b/tools/libxl/libxl_domain.c
@@ -1179,6 +1179,14 @@ void libxl__destroy_domid(libxl__egc *egc, libxl__destroy_domid_state *dis)
         goto out;
     }
 
+    /*
+     * Only possible errors are unrecoverable xenstore transaction
+     * errors.
+     */
+    rc = libxl__sshm_del(gc, domid);
+    if (rc)
+        LOGD(ERROR, domid, "Deleting static shm failed.");
+
     libxl__multidev_begin(ao, &dis->multidev);
     dis->multidev.callback = destroy_domid_pci_done;
     libxl__device_pci_destroy_all(egc, domid, &dis->multidev);

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 72715da5635f59a08658dd649b6df692b6b7667b..d8217d0d8f1a64d298e6c3c72db608322a8ab34b 100644 (file)
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -4783,6 +4783,8 @@ _hidden int libxl__domain_pvcontrol(libxl__egc *egc,
 _hidden int libxl__sshm_add(libxl__gc *gc, uint32_t domid,
                             libxl_static_shm *sshm, int len);
 
+_hidden int libxl__sshm_del(libxl__gc *gc, uint32_t domid);
+
 _hidden int libxl__sshm_check_overlap(libxl__gc *gc, uint32_t domid,
                                       libxl_static_shm *sshms, int len);
 _hidden int libxl__sshm_setdefault(libxl__gc *gc, uint32_t domid,

diff --git a/tools/libxl/libxl_sshm.c b/tools/libxl/libxl_sshm.c
index 37944cfa56fedf5ee58993075c4bef30ee1dc5f9..8d0c2d2ed6e4a6bc5a5f54a2ab549989d4bf8f0b 100644 (file)
--- a/tools/libxl/libxl_sshm.c
+++ b/tools/libxl/libxl_sshm.c
@@ -94,6 +94,137 @@ int libxl__sshm_check_overlap(libxl__gc *gc, uint32_t domid,
     return 0;
 }
 
+/*
+ * Decrease the refcount of an sshm. When refcount reaches 0,
+ * clean up the whole sshm path.
+ * Xenstore operations are done within the same transaction.
+ */
+static void libxl__sshm_decref(libxl__gc *gc, xs_transaction_t xt,
+                               const char *sshm_path)
+{
+    int count;
+    const char *count_path, *count_string;
+
+    count_path = GCSPRINTF("%s/usercnt", sshm_path);
+    if (libxl__xs_read_checked(gc, xt, count_path, &count_string) ||
+        count_string == NULL)
+        return;
+    count = atoi(count_string);
+
+    if (--count == 0) {
+        libxl__xs_path_cleanup(gc, xt, sshm_path);
+        return;
+    }
+
+    count_string = GCSPRINTF("%d", count);
+    libxl__xs_write_checked(gc, xt, count_path, count_string);
+
+    return;
+}
+
+static void libxl__sshm_do_unmap(libxl__gc *gc, uint32_t domid, const char *id,
+                                 uint64_t begin, uint64_t size)
+{
+    uint64_t end;
+    begin >>= XC_PAGE_SHIFT;
+    size >>= XC_PAGE_SHIFT;
+    end = begin + size;
+    for (; begin < end; ++begin) {
+        if (xc_domain_remove_from_physmap(CTX->xch, domid, begin)) {
+            SSHM_ERROR(domid, id,
+                       "unable to unmap shared page at 0x%"PRIx64".",
+                       begin);
+        }
+    }
+}
+
+/* unmap static shared memory areas mapped by libxl__sshm_add */
+static void libxl__sshm_del_borrower(libxl__gc *gc, xs_transaction_t xt,
+                                     uint32_t domid, const char *id)
+{
+    const char *borrower_path, *begin_str, *size_str;
+    uint64_t begin, size;
+
+    borrower_path = GCSPRINTF("%s/borrowers/%"PRIu32, SSHM_PATH(id), domid);
+
+    begin_str = libxl__xs_read(gc, xt, GCSPRINTF("%s/begin", borrower_path));
+    size_str = libxl__xs_read(gc, xt, GCSPRINTF("%s/size", borrower_path));
+    begin = strtoull(begin_str, NULL, 16);
+    size = strtoull(size_str, NULL, 16);
+
+    libxl__sshm_do_unmap(gc, domid, id, begin, size);
+    libxl__xs_path_cleanup(gc, xt, borrower_path);
+}
+
+/*
+ * Add libxl__sshm_del to unmap static shared memory areas mapped by
+ * libxl__sshm_add during domain creation. The unmapping process is:
+ *
+ * For a owner: decrease the refcount of the sshm region, if the refcount
+ * reaches 0, cleanup the whole sshm path.
+ *
+ * For a borrower:
+ * 1) unmap the shared pages, and cleanup related xs entries. If the
+ *    system works normally, all the shared pages will be unmapped, so there
+ *    won't be page leaks. In case of errors, the unmapping process will go
+ *    on and unmap all the other pages that can be unmapped, so the other
+ *    pages won't be leaked, either.
+ * 2) Decrease the refcount of the sshm region, if the refcount reaches
+ *    0, cleanup the whole sshm path.
+ */
+int libxl__sshm_del(libxl__gc *gc,  uint32_t domid)
+{
+    int rc, i;
+    xs_transaction_t xt = XBT_NULL;
+    const char *dom_path, *dom_sshm_path, *role;
+    char **sshm_ents;
+    unsigned int sshm_num;
+
+    dom_path = libxl__xs_get_dompath(gc, domid);
+    dom_sshm_path = GCSPRINTF("%s/static_shm", dom_path);
+
+    for (;;) {
+        rc = libxl__xs_transaction_start(gc, &xt);
+        if (rc) goto out;
+
+        sshm_ents = libxl__xs_directory(gc, xt, dom_sshm_path, &sshm_num);
+        if (!sshm_ents) {
+            if (errno != ENOENT) {
+                LOGE(ERROR, "unable to get xenstore device listing %s",
+                     dom_sshm_path);
+                goto out;
+            }
+            break;
+        }
+
+        for (i = 0; i < sshm_num; ++i) {
+            role = libxl__xs_read(gc, xt,
+                    GCSPRINTF("%s/%s/role",
+                        dom_sshm_path,
+                        sshm_ents[i]));
+            assert(role);
+            if (!strncmp(role, "borrower", 8))
+                libxl__sshm_del_borrower(gc, xt, domid, sshm_ents[i]);
+            else if (strncmp(role, "owner", 5)) {
+                rc = ERROR_INVAL;
+                goto out;
+            }
+
+
+            libxl__sshm_decref(gc, xt, SSHM_PATH(sshm_ents[i]));
+        }
+
+        rc = libxl__xs_transaction_commit(gc, &xt);
+        if (!rc) break;
+        if (rc < 0) goto out;
+    }
+
+    rc = 0;
+out:
+    libxl__xs_transaction_abort(gc, &xt);
+    return rc;
+}
+
 /*   libxl__sshm_do_map -- map pages into borrower's physmap
  *
  *   This functions maps