[PATCH v2 6/6] libxl: support unmapping static shared memory areas during domain destruction

[Zhongze Liu <blackskygg@gmail.com>]

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

* For a master: decrease the refcount of the sshm region, if the refcount
  reaches 0, cleanup the whole sshm path.
* For a slave: unmap the shared pages, and cleanup related xs entries.
  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>

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
---
v2:
  * use the predefined XC_PAGE_SIZE instead of hardcoding 12
  * refcounting the node
---
 tools/libxl/libxl_domain.c   |   5 +++
 tools/libxl/libxl_internal.h |   2 +
 tools/libxl/libxl_sshm.c     | 105 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 112 insertions(+)

diff --git a/tools/libxl/libxl_domain.c b/tools/libxl/libxl_domain.c
index 08eccd082b..73ac856fb4 100644
--- a/tools/libxl/libxl_domain.c
+++ b/tools/libxl/libxl_domain.c
@@ -1028,6 +1028,11 @@ void libxl__destroy_domid(libxl__egc *egc, libxl__destroy_domid_state *dis)
         goto out;
     }
 
+    rc = libxl__sshm_del(gc, domid);
+    if (rc) {
+        LOGD(ERROR, domid, "Deleting static shm failed.");
+    }
+
     if (libxl__device_pci_destroy_all(gc, domid) < 0)
         LOGD(ERROR, domid, "Pci shutdown failed");
     rc = xc_domain_pause(ctx->xch, domid);
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 7ab2d40c49..731823dc1e 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -4360,6 +4360,8 @@ static inline bool libxl__acpi_defbool_val(const libxl_domain_build_info *b_info
 _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 a4091a3056..edfde0a905 100644
--- a/tools/libxl/libxl_sshm.c
+++ b/tools/libxl/libxl_sshm.c
@@ -86,6 +86,111 @@ 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 */
+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/users", sshm_path);
+    if (libxl__xs_read_checked(gc, xt, count_path, &count_string))
+        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 end)
+{
+    begin >>= XC_PAGE_SHIFT;
+    end >>= XC_PAGE_SHIFT;
+    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);
+        }
+    }
+}
+
+static void libxl__sshm_del_slave(libxl__gc *gc, xs_transaction_t xt,
+                                  uint32_t domid, const char *id, bool isretry)
+{
+    const char *slave_path, *begin_str, *end_str;
+    uint64_t begin, end;
+
+    slave_path = GCSPRINTF("%s/slaves/%"PRIu32, SSHM_PATH(id), domid);
+
+    begin_str = libxl__xs_read(gc, xt, GCSPRINTF("%s/begin", slave_path));
+    end_str = libxl__xs_read(gc, xt, GCSPRINTF("%s/end", slave_path));
+    begin = strtoull(begin_str, NULL, 16);
+    end = strtoull(end_str, NULL, 16);
+
+    /* Avoid calling do_unmap many times in case of xs transaction retry */
+    if (!isretry)
+        libxl__sshm_do_unmap(gc, domid, id, begin, end);
+
+    libxl__xs_path_cleanup(gc, xt, slave_path);
+}
+
+/* Delete static_shm entries in the xensotre. */
+int libxl__sshm_del(libxl__gc *gc,  uint32_t domid)
+{
+    int rc, i;
+    bool isretry;
+    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);
+
+    isretry = false;
+    for (;;) {
+        rc = libxl__xs_transaction_start(gc, &xt);
+        if (rc) goto out;
+
+        if (libxl__xs_read(gc, xt, dom_sshm_path)) {
+            sshm_ents = libxl__xs_directory(gc, xt, dom_sshm_path, &sshm_num);
+            if (!sshm_ents) continue;
+
+            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, "slave", 5))
+                    libxl__sshm_del_slave(gc, xt, domid, sshm_ents[i], isretry);
+
+                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;
+         isretry = true;
+    }
+
+    rc = 0;
+out:
+    libxl__xs_transaction_abort(gc, &xt);
+    return rc;
+}
+
 /* The caller have to guarentee that sshm->begin < sshm->end */
 static int libxl__sshm_do_map(libxl__gc *gc, uint32_t mid, uint32_t sid,
                               libxl_static_shm *sshm,
-- 
2.14.0


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