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[PATCH v2] kexec-xen: Allow xen_kexec_exec() to return in case of Live Update



From: Raphael Ning <raphning@xxxxxxxxxx>

Currently, my_exec() does not expect the Xen KEXEC_CMD_kexec hypercall
to return on success, because it assumes that the hypercall always
triggers an immediate reboot. However, for Live Update, the hypercall
merely schedules the kexec operation and returns; the actual reboot
happens asynchronously. [1]

Therefore, rework the Xen code path of my_exec() such that it does not
treat a successfully processed Live Update request as an error. Also,
rephrase the comment above the function to remove ambiguity.

[1] https://lists.xen.org/archives/html/xen-devel/2021-05/msg00286.html

Signed-off-by: Raphael Ning <raphning@xxxxxxxxxx>
---
Changes in v2:
- Fix --without-xen build.

---
 kexec/kexec-xen.c | 12 ++++++++----
 kexec/kexec.c     | 23 +++++++++++++++++++----
 kexec/kexec.h     |  2 +-
 3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/kexec/kexec-xen.c b/kexec/kexec-xen.c
index 47da3da466f0..a7c89339c4b7 100644
--- a/kexec/kexec-xen.c
+++ b/kexec/kexec-xen.c
@@ -247,21 +247,24 @@ int xen_kexec_status(uint64_t kexec_flags)
        return ret;
 }
 
-void xen_kexec_exec(uint64_t kexec_flags)
+int xen_kexec_exec(uint64_t kexec_flags)
 {
        xc_interface *xch;
        uint8_t type = KEXEC_TYPE_DEFAULT;
+       int ret;
 
        xch = xc_interface_open(NULL, NULL, 0);
        if (!xch)
-               return;
+               return -1;
 
        if (kexec_flags & KEXEC_LIVE_UPDATE)
                type = KEXEC_TYPE_LIVE_UPDATE;
 
-       xc_kexec_exec(xch, type);
+       ret = xc_kexec_exec(xch, type);
 
        xc_interface_close(xch);
+
+       return ret;
 }
 
 #else /* ! HAVE_LIBXENCTRL */
@@ -286,8 +289,9 @@ int xen_kexec_status(uint64_t kexec_flags)
        return -1;
 }
 
-void xen_kexec_exec(uint64_t kexec_flags)
+int xen_kexec_exec(uint64_t kexec_flags)
 {
+       return -1;
 }
 
 #endif
diff --git a/kexec/kexec.c b/kexec/kexec.c
index 7e4787bc8211..e7861049bbea 100644
--- a/kexec/kexec.c
+++ b/kexec/kexec.c
@@ -902,13 +902,28 @@ static int my_shutdown(void)
 }
 
 /*
- *     Exec the new kernel (reboot)
+ *     Exec the new kernel. If successful, this triggers an immediate reboot
+ *     and does not return, but Xen Live Update is an exception (more on this
+ *     below).
  */
 static int my_exec(void)
 {
-       if (xen_present())
-               xen_kexec_exec(kexec_flags);
-       else
+       if (xen_present()) {
+               int ret;
+
+               /*
+                * There are two cases in which the Xen hypercall may return:
+                * 1) An error occurred, e.g. the kexec image was not loaded.
+                *    The exact error is indicated by errno.
+                * 2) Live Update was successfully scheduled. Note that unlike
+                *    a normal kexec, Live Update happens asynchronously, i.e.
+                *    the hypercall merely schedules the kexec operation and
+                *    returns immediately.
+                */
+               ret = xen_kexec_exec(kexec_flags);
+               if ((kexec_flags & KEXEC_LIVE_UPDATE) && !ret)
+                       return 0;
+       } else
                reboot(LINUX_REBOOT_CMD_KEXEC);
        /* I have failed if I make it here */
        fprintf(stderr, "kexec failed: %s\n", 
diff --git a/kexec/kexec.h b/kexec/kexec.h
index 595dd681db6d..0f97a974cb8a 100644
--- a/kexec/kexec.h
+++ b/kexec/kexec.h
@@ -324,7 +324,7 @@ void cmdline_add_liveupdate(char **base);
 int xen_present(void);
 int xen_kexec_load(struct kexec_info *info);
 int xen_kexec_unload(uint64_t kexec_flags);
-void xen_kexec_exec(uint64_t kexec_flags);
+int xen_kexec_exec(uint64_t kexec_flags);
 int xen_kexec_status(uint64_t kexec_flags);
 
 extern unsigned long long get_kernel_sym(const char *text);
-- 
2.32.0




 


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