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

[Zhongze Liu <blackskygg@xxxxxxxxx>]

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: check if it still has living slaves: 1) if yes, mark its
  status as "zombie", and don't destroy the information under
  /local/static_shm; 2) if no, simply cleanup related xs entries
* For a slave: unmap the shared pages, and cleanup related xs entries. If
  this is the only slave, and it's master is in zombie state, also cleanup
  the master entries.

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

[1] https://lists.xenproject.org/archives/html/xen-devel/2017-07/msg03047.html

Signed-off-by: Zhongze Liu <blackskygg@xxxxxxxxx>

Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxx
---
 tools/libxl/libxl_domain.c   |   5 ++
 tools/libxl/libxl_internal.h |   2 +
 tools/libxl/libxl_sshm.c     | 125 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 132 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 74bc0acb21..648eaee8c2 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -4361,6 +4361,8 @@ 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 e16c24ccb9..417a4cd0a4 100644
--- a/tools/libxl/libxl_sshm.c
+++ b/tools/libxl/libxl_sshm.c
@@ -79,6 +79,131 @@ int libxl__sshm_check_overlap(libxl__gc *gc, uint32_t domid,
     return 0;
 }
 
+/* Delete sshm master infomation from xenstore. If there are still living
+ * slaves, mark the master as in zombie state, but do not delete it,
+ * and it will be totally deleted later after all slaves are gone */
+static void libxl__sshm_del_master(libxl__gc *gc, xs_transaction_t xt,
+                                   uint32_t domid, const char *id)
+{
+    char *sshm_path;
+
+    sshm_path = libxl__xs_get_sshmpath(gc, id);
+
+    /* we know that domid can't be both a master and a slave for one id
+     * (enforced in the *_add_master() and *_add_slave() code),
+     * so the number of slaves won't change during iteration. Simply check
+     * sshm_path/slaves to tell if there are still living slaves. */
+    if (libxl__xs_read(gc, xt, GCSPRINTF("%s/slaves", sshm_path))) {
+        SSHM_ERROR(domid, id,
+                   "there are living slaves, won't be totally destroyed");
+
+        libxl__xs_write_checked(gc, xt,
+                                GCSPRINTF("%s/status", sshm_path),
+                                "zombie");
+    } else {
+        libxl__xs_path_cleanup(gc, xt, sshm_path);
+    }
+
+    return;
+}
+
+static void libxl__sshm_do_unmap(libxl__gc *gc, uint32_t domid, const char *id,
+                                 uint64_t begin, uint64_t end)
+{
+    begin >>= 12;
+    end >>= 12;
+    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)
+{
+    char *sshm_path, *slave_path;
+    char *master_stat, *mdomid_str, *begin_str, *end_str;
+    uint64_t begin, end;
+    uint32_t master_domid;
+
+    sshm_path = libxl__xs_get_sshmpath(gc, id);
+    slave_path = GCSPRINTF("%s/slaves/%"PRIu32, sshm_path, 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);
+
+    /* check if master is in zombie state and has no slaves now,
+     * if yes, now it's the time to destroy it */
+    master_stat = libxl__xs_read(gc, xt, GCSPRINTF("%s/status", sshm_path));
+    if (!strncmp(master_stat, "zombie", 6) &&
+        !libxl__xs_read(gc, xt, GCSPRINTF("%s/slaves", sshm_path)))
+    {
+        mdomid_str = libxl__xs_read(gc, xt, GCSPRINTF("%s/master", sshm_path));
+        master_domid = strtoul(mdomid_str, NULL, 10);
+        libxl__sshm_del_master(gc, xt, master_domid, id);
+    }
+}
+
+/* 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;
+    char *dom_path, *dom_sshm_path;
+    const char *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);
+                } else {
+                    libxl__sshm_del_master(gc, xt, domid, 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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