[Xen-devel] [PATCH v4] kexec: implement STATUS hypercall to check if image is loaded

[Eric DeVolder <eric.devolder@xxxxxxxxxx>]

The tools that use kexec are asynchronous in nature and do not keep
state changes. As such provide an hypercall to find out whether an
image has been loaded for either type.

Note: No need to modify XSM as it has one size fits all check and
does not check for subcommands.

Note: No need to check KEXEC_FLAG_IN_PROGRESS (and error out of
kexec_status()) as this flag is set only once by the first/only
cpu on the crash path.

Note: In kexec_status(), the use of test_bit() can also return
EPERM, so the return value from test_bit() must be checked to
ensure that kexec_status() always returns 0, 1 or -1, per the
public header description.

Note: This is just the Xen side of the hypercall, kexec-tools patch
to come separately.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
---
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>
CC: Daniel Kiper <daniel.kiper@xxxxxxxxxx>

v0: Internal version.
v1: Dropped Reviewed-by, posting on xen-devel.
v2: Incorporated xen-devel feedback, re-posted on xen-devel.
v3: Incorporated xen-devel feedback, re-posted on xen-devel.
v4: Incorporated xen-devel feedback
---
 tools/libxc/include/xenctrl.h | 10 ++++++++++
 tools/libxc/xc_kexec.c        | 24 ++++++++++++++++++++++++
 xen/common/kexec.c            | 19 +++++++++++++++++++
 xen/include/public/kexec.h    | 14 ++++++++++++++
 4 files changed, 67 insertions(+)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index 4ab0f57..63c616f 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -2574,6 +2574,16 @@ int xc_kexec_load(xc_interface *xch, uint8_t type, 
uint16_t arch,
  */
 int xc_kexec_unload(xc_interface *xch, int type);
 
+/*
+ * Find out whether the image has been succesfully loaded.
+ *
+ * The type can be either KEXEC_TYPE_DEFAULT or KEXEC_TYPE_CRASH.
+ * If zero is returned, that means no image is loaded for the type.
+ * If one is returned, that means an image is loaded for the type.
+ * Otherwise, negative return value indicates error.
+ */
+int xc_kexec_status(xc_interface *xch, int type);
+
 typedef xenpf_resource_entry_t xc_resource_entry_t;
 
 /*
diff --git a/tools/libxc/xc_kexec.c b/tools/libxc/xc_kexec.c
index 59e2f07..a4e8966 100644
--- a/tools/libxc/xc_kexec.c
+++ b/tools/libxc/xc_kexec.c
@@ -126,3 +126,27 @@ out:
 
     return ret;
 }
+
+int xc_kexec_status(xc_interface *xch, int type)
+{
+    DECLARE_HYPERCALL_BUFFER(xen_kexec_status_t, status);
+    int ret = -1;
+
+    status = xc_hypercall_buffer_alloc(xch, status, sizeof(*status));
+    if ( status == NULL )
+    {
+        PERROR("Could not alloc buffer for kexec status hypercall");
+        goto out;
+    }
+
+    status->type = type;
+
+    ret = xencall2(xch->xcall, __HYPERVISOR_kexec_op,
+                   KEXEC_CMD_kexec_status,
+                   HYPERCALL_BUFFER_AS_ARG(status));
+
+out:
+    xc_hypercall_buffer_free(xch, status);
+
+    return ret;
+}
diff --git a/xen/common/kexec.c b/xen/common/kexec.c
index c83d48f..40b76d5 100644
--- a/xen/common/kexec.c
+++ b/xen/common/kexec.c
@@ -1169,6 +1169,22 @@ static int kexec_unload(XEN_GUEST_HANDLE_PARAM(void) 
uarg)
     return kexec_do_unload(&unload);
 }
 
+static int kexec_status(XEN_GUEST_HANDLE_PARAM(void) uarg)
+{
+    xen_kexec_status_t status;
+    int base, bit;
+
+    if ( unlikely(copy_from_guest(&status, uarg, 1)) )
+        return -EFAULT;
+
+    /* No need to check KEXEC_FLAG_IN_PROGRESS. */
+
+    if ( kexec_load_get_bits(status.type, &base, &bit) )
+        return -EINVAL;
+
+    return (test_bit(bit, &kexec_flags) == 1);
+}
+
 static int do_kexec_op_internal(unsigned long op,
                                 XEN_GUEST_HANDLE_PARAM(void) uarg,
                                 bool_t compat)
@@ -1208,6 +1224,9 @@ static int do_kexec_op_internal(unsigned long op,
     case KEXEC_CMD_kexec_unload:
         ret = kexec_unload(uarg);
         break;
+    case KEXEC_CMD_kexec_status:
+        ret = kexec_status(uarg);
+        break;
     }
 
     return ret;
diff --git a/xen/include/public/kexec.h b/xen/include/public/kexec.h
index a6a0a88..74ea981 100644
--- a/xen/include/public/kexec.h
+++ b/xen/include/public/kexec.h
@@ -227,6 +227,20 @@ typedef struct xen_kexec_unload {
 } xen_kexec_unload_t;
 DEFINE_XEN_GUEST_HANDLE(xen_kexec_unload_t);
 
+/*
+ * Figure out whether we have an image loaded. A return value of
+ * zero indicates no image loaded. A return value of one
+ * indicates an image is loaded. A negative return value
+ * indicates an error.
+ *
+ * Type must be one of KEXEC_TYPE_DEFAULT or KEXEC_TYPE_CRASH.
+ */
+#define KEXEC_CMD_kexec_status 6
+typedef struct xen_kexec_status {
+    uint8_t type;
+} xen_kexec_status_t;
+DEFINE_XEN_GUEST_HANDLE(xen_kexec_status_t);
+
 #else /* __XEN_INTERFACE_VERSION__ < 0x00040400 */
 
 #define KEXEC_CMD_kexec_load KEXEC_CMD_kexec_load_v1
-- 
2.7.4


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