[PATCH v2] igvm: add command line parameter support

[Luigi Leonardi <leonardi@redhat.com>]

Add a "cmdline" property to the igvm-cfg object and a handler for the
IGVM_VHT_COMMAND_LINE directive, which copies the string into the
parameter area the directive points at.

The command line is passed to whatever software the IGVM file loads,
such as an SVSM. For example, SVSM can use it to select the serial port
it logs to.

Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
---
Changes in v2:
- Updated commit message and doc to make it clear that QEMU does not
  need to parse this string [Markus]
- Link to v1: https://lore.kernel.org/qemu-devel/20260930-igvm_command_line-v1-1-62857007d89d@redhat.com
---
 backends/igvm-cfg.c            | 21 +++++++++++++++++++++
 backends/igvm.c                | 31 +++++++++++++++++++++++++++++++
 include/system/igvm-internal.h |  5 +++++
 qapi/qom.json                  |  6 +++++-
 4 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/backends/igvm-cfg.c b/backends/igvm-cfg.c
index 935ba54f54..ec796ea8a6 100644
--- a/backends/igvm-cfg.c
+++ b/backends/igvm-cfg.c
@@ -34,6 +34,19 @@ static void set_igvm(Object *obj, const char *value, Error **errp)
     igvm->filename = g_strdup(value);
 }
 
+static char *get_cmdline(Object *obj, Error **errp)
+{
+    IgvmCfg *igvm = IGVM_CFG(obj);
+    return g_strdup(igvm->cmdline);
+}
+
+static void set_cmdline(Object *obj, const char *value, Error **errp)
+{
+    IgvmCfg *igvm = IGVM_CFG(obj);
+    g_free(igvm->cmdline);
+    igvm->cmdline = g_strdup(value);
+}
+
 static ResettableState *igvm_reset_state(Object *obj)
 {
     IgvmCfg *igvm = IGVM_CFG(obj);
@@ -85,6 +98,13 @@ static void igvm_cfg_class_init(ObjectClass *oc, const void *data)
     object_class_property_set_description(oc, "file",
                                           "Set the IGVM filename to use");
 
+    object_class_property_add_str(oc, "cmdline", get_cmdline, set_cmdline);
+    object_class_property_set_description(oc, "cmdline",
+                                          "Set the kernel-style command line "
+                                          "for the software loaded from the IGVM "
+                                          "file (copied verbatim, not "
+                                          "parsed by QEMU)");
+
     igvmc->process = qigvm_process_file;
 
     rc->get_state = igvm_reset_state;
@@ -112,4 +132,5 @@ static void igvm_cfg_finalize(Object *obj)
         igvm_free(igvm->file);
     }
     g_free(igvm->filename);
+    g_free(igvm->cmdline);
 }
diff --git a/backends/igvm.c b/backends/igvm.c
index ec7bee428b..d059fee4d2 100644
--- a/backends/igvm.c
+++ b/backends/igvm.c
@@ -158,6 +158,8 @@ static int qigvm_directive_snp_id_block(QIgvm *ctx, const uint8_t *header_data,
 static int qigvm_initialization_guest_policy(QIgvm *ctx,
                                        const uint8_t *header_data,
                                        Error **errp);
+static int qigvm_directive_command_line(QIgvm *ctx, const uint8_t *header_data,
+                                        Error **errp);
 #ifdef CONFIG_FDT
 static int qigvm_directive_device_tree(QIgvm *ctx, const uint8_t *header_data,
                                        Error **errp);
@@ -192,6 +194,8 @@ static struct QIGVMHandler handlers[] = {
       qigvm_initialization_guest_policy },
     { IGVM_VHT_MADT, IGVM_HEADER_SECTION_DIRECTIVE,
       qigvm_directive_madt },
+    { IGVM_VHT_COMMAND_LINE, IGVM_HEADER_SECTION_DIRECTIVE,
+      qigvm_directive_command_line },
 #ifdef CONFIG_FDT
     { IGVM_VHT_DEVICE_TREE, IGVM_HEADER_SECTION_DIRECTIVE,
       qigvm_directive_device_tree },
@@ -851,6 +855,33 @@ static int qigvm_directive_snp_id_block(QIgvm *ctx, const uint8_t *header_data,
     return 0;
 }
 
+static int qigvm_directive_command_line(QIgvm *ctx, const uint8_t *header_data,
+                                        Error **errp)
+{
+    const IGVM_VHS_PARAMETER *param = (const IGVM_VHS_PARAMETER *)header_data;
+    const char *cmdline = ctx->cfg->cmdline ? ctx->cfg->cmdline : "";
+    uint8_t *param_data;
+    uint32_t param_size;
+    size_t cmdline_size = strlen(cmdline) + 1;
+
+    param_data = qigvm_get_param_data(ctx, param, &param_size, errp);
+    if (!param_data) {
+        return -1;
+    }
+
+    if (cmdline_size > param_size) {
+        error_setg(errp,
+                   "IGVM: command line size %zu exceeds the %u byte "
+                   "parameter area defined in IGVM file",
+                   cmdline_size, param_size);
+        return -1;
+    }
+
+    memcpy(param_data, cmdline, cmdline_size);
+
+    return 0;
+}
+
 #ifdef CONFIG_FDT
 static int qigvm_directive_device_tree(QIgvm *ctx, const uint8_t *header_data,
                                        Error **errp)
diff --git a/include/system/igvm-internal.h b/include/system/igvm-internal.h
index b3b64cb584..b56a2e1254 100644
--- a/include/system/igvm-internal.h
+++ b/include/system/igvm-internal.h
@@ -32,6 +32,11 @@ struct IgvmCfg {
      *           format.
      */
     char *filename;
+    /*
+     * cmdline: Command line for the software loaded from the IGVM file,
+     *          if it asks for one.
+     */
+    char *cmdline;
     IgvmHandle file;
     ResettableState reset_state;
     QTAILQ_HEAD(, IgvmMemoryRegion) memory_regions;
diff --git a/qapi/qom.json b/qapi/qom.json
index 5895c97750..1823ece665 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -1004,11 +1004,15 @@
 #
 # @file: IGVM file to use to configure guest
 #
+# @cmdline: kernel-style command line for the software loaded from
+#     the IGVM file.  Passed verbatim: QEMU does not parse it.
+#     Ignored if the IGVM file does not ask for one.  (since 11.2)
+#
 # Since: 10.1
 ##
 { 'struct': 'IgvmCfgProperties',
   'if': 'CONFIG_IGVM',
-  'data': { 'file': 'str' } }
+  'data': { 'file': 'str', '*cmdline': 'str' } }
 
 ##
 # @SevCommonProperties:

---
base-commit: 9c88811b81a935a172c5c873b2ada2d9b38a5f74
change-id: 20260930-igvm_command_line-ccb5a0bddda0

Best regards,
-- 
Luigi Leonardi <leonardi@redhat.com>