[Xen-devel] [PATCH v2] 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: The __XEN_LATEST_INTERFACE_VERSION__ has been bumped to
0x00040900 due to the introduction of a new hypervisor call.

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>
Reviewed-by: Daniel Kiper <daniel.kiper@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
---
 tools/libxc/include/xenctrl.h   | 10 ++++++++++
 tools/libxc/xc_kexec.c          | 24 ++++++++++++++++++++++++
 xen/common/kexec.c              | 19 +++++++++++++++++++
 xen/include/public/kexec.h      | 13 +++++++++++++
 xen/include/public/xen-compat.h |  2 +-
 5 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index 4ab0f57117..63c616ff6a 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 989e225192..a0a9fd3841 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 c83d48fc79..aa808cb2f2 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);
+}
+
 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 a6a0a88f4f..c200e8ceee 100644
--- a/xen/include/public/kexec.h
+++ b/xen/include/public/kexec.h
@@ -227,6 +227,19 @@ 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
diff --git a/xen/include/public/xen-compat.h b/xen/include/public/xen-compat.h
index dd8a5c0d0e..b67365340b 100644
--- a/xen/include/public/xen-compat.h
+++ b/xen/include/public/xen-compat.h
@@ -27,7 +27,7 @@
 #ifndef __XEN_PUBLIC_XEN_COMPAT_H__
 #define __XEN_PUBLIC_XEN_COMPAT_H__
 
-#define __XEN_LATEST_INTERFACE_VERSION__ 0x00040800
+#define __XEN_LATEST_INTERFACE_VERSION__ 0x00040900
 
 #if defined(__XEN__) || defined(__XEN_TOOLS__)
 /* Xen is built with matching headers and implements the latest interface. */
-- 
2.11.0


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