Re: [PATCH v3 6/6] igvm: Fill MADT IGVM parameter field

[Luigi Leonardi]

On Fri, Jan 09, 2026 at 03:34:13PM +0100, Oliver Steffen wrote:

Use the new acpi_build_madt_standalone() function to fill the MADT
parameter field.

The IGVM parameter can be consumed by Coconut SVSM [1], instead of
relying on the fw_cfg interface, which has caused problems before due to
unexpected access [2,3]. Using IGVM parameters is the default way for
Coconut SVSM; switching over would allow removing specialized code paths
for QEMU in Coconut.

In any case OVMF, which runs after SVSM has already been initialized,
will continue reading all ACPI tables via fw_cfg and provide fixed up
ACPI data to the OS as before.

Generating the MADT twice (during ACPI table building and IGVM processing)
seems acceptable, since there is no infrastructure to obtain the MADT
out of the ACPI table memory area.

[1] https://github.com/coconut-svsm/svsm/pull/858
[2] https://gitlab.com/qemu-project/qemu/-/issues/2882
[3] https://github.com/coconut-svsm/svsm/issues/646

Signed-off-by: Oliver Steffen <ostef...@redhat.com>

SQUASH: Rename madt parameter handler

Development leftover?

---
backends/igvm.c | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)

diff --git a/backends/igvm.c b/backends/igvm.c
index 7390dee734..90ea2c22fd 100644
--- a/backends/igvm.c
+++ b/backends/igvm.c
@@ -15,9 +15,11 @@
#include "qapi/error.h"
#include "qemu/target-info-qapi.h"
#include "system/igvm.h"
+#include "glib.h"

is this needed?

#include "system/memory.h"
#include "system/address-spaces.h"
#include "hw/core/cpu.h"
+#include "hw/i386/acpi-build.h"

#include "trace.h"

@@ -134,6 +136,8 @@ 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_madt(QIgvm *ctx,
+                                     const uint8_t *header_data, Error **errp);

struct QIGVMHandler {
    uint32_t type;
@@ -162,6 +166,8 @@ static struct QIGVMHandler handlers[] = {
      qigvm_directive_snp_id_block },
    { IGVM_VHT_GUEST_POLICY, IGVM_HEADER_SECTION_INITIALIZATION,
      qigvm_initialization_guest_policy },
+    { IGVM_VHT_MADT, IGVM_HEADER_SECTION_DIRECTIVE,
+      qigvm_directive_madt },
};

static int qigvm_handler(QIgvm *ctx, uint32_t type, Error **errp)
@@ -780,6 +786,35 @@ static int qigvm_initialization_guest_policy(QIgvm *ctx,
    return 0;
}

+static int qigvm_directive_madt(QIgvm *ctx,
+                                     const uint8_t *header_data, Error **errp)
+{
+    const IGVM_VHS_PARAMETER *param = (const IGVM_VHS_PARAMETER *)header_data;
+    QIgvmParameterData *param_entry;
+
+    if (ctx->machine_state == NULL) {
+        return 0;
+    }
+
+    /* Find the parameter area that should hold the MADT data */
+    param_entry = qigvm_find_param_entry(ctx, param);
+    if (param_entry != NULL) {
+
+        GArray *madt = acpi_build_madt_standalone(ctx->machine_state);
+
+        if (madt->len > param_entry->size) {
+            error_setg(
+                errp,
+                "IGVM: MADT size exceeds parameter area defined in IGVM file");
+            return -1;
+        }
+        memcpy(param_entry->data, madt->data, madt->len);
+
+        g_array_free(madt, true);
+    }
+    return 0;
+}
+
static int qigvm_supported_platform_compat_mask(QIgvm *ctx, Error **errp)
{
    int32_t header_count;
--
2.52.0

Rest LGTM!

Luigi