hw/tpm: Add support for VM migration with TPM CRB chunking
- Add subsection in VMState for TPM CRB with the newly introduced command and response buffer GByteArrays, along with a needed callback, so that newer QEMU only sends the buffers if it is necessary. - Implement a migration blocker to prevent migration of the VM if the user manually enables chunking capability, cap-chunk, but the machine type does not support it, using a new hw_compat property called allow_chunk_migration. - Add a post_load_errp hook so that during a migration, the buffers are validated before destination VM is started. Signed-off-by: Arun Menon <armenon@redhat.com> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com> Link: https://lore.kernel.org/qemu-devel/20260506075813.120781-7-armenon@redhat.com Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Arun Menon committed
May 6, 2026 at 13:28 UTC
a8aa1b220c71442bac961bdafa64da8b9604686b
2 files changed
+68
hw/core/machine.c
+1
@@ -42,6 +42,7 @@
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GlobalProperty hw_compat_11_0[] = {
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{ "chardev-vc", "encoding", "cp437" },
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{ "tpm-crb", "cap-chunk", "off" },
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+ { "tpm-crb", "x-allow-chunk-migration", "off" },
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};
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const size_t hw_compat_11_0_len = G_N_ELEMENTS(hw_compat_11_0);
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hw/tpm/tpm_crb.c
+67
@@ -24,6 +24,7 @@
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#include "hw/pci/pci_ids.h"
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#include "hw/acpi/tpm.h"
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#include "migration/vmstate.h"
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+#include "migration/blocker.h"
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#include "system/tpm_backend.h"
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#include "system/tpm_util.h"
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#include "system/reset.h"
@@ -50,6 +51,8 @@ struct CRBState {
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TPMPPI ppi;
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bool cap_chunk;
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+ bool allow_chunk_migration;
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+ Error *migration_blocker;
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};
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typedef struct CRBState CRBState;
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@@ -349,18 +352,68 @@ static int tpm_crb_pre_save(void *opaque)
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return 0;
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}
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+static bool tpm_crb_chunk_needed(void *opaque)
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+{
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+ CRBState *s = opaque;
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+
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+ if (!s->allow_chunk_migration) {
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+ return false;
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+ }
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+
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+ return ((s->command_buffer && s->command_buffer->len > 0) ||
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+ (s->response_buffer && s->response_buffer->len > 0));
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+}
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+
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+static bool tpm_crb_chunk_post_load(void *opaque, int version_id, Error **errp)
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+{
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+ CRBState *s = opaque;
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+
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+ /*
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+ * The external TPM emulator (example swtpm) determines the backend
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+ * buffer capacity (s->be_buffer_size). This check ensures that if we
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+ * migrate from a source with a PQC-enabled emulator that supports
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+ * larger buffers to a destination with a non-PQC emulator, the
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+ * migrated data does not exceed the destination's capacity.
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+ */
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+ if (s->response_buffer->len > s->be_buffer_size ||
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+ s->command_buffer->len > s->be_buffer_size) {
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+ error_setg(errp, "tpm-crb: Buffer sizes exceed backend capacity");
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+ return false;
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+ }
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+ return true;
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+}
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+
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+static const VMStateDescription vmstate_tpm_crb_chunk = {
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+ .name = "tpm-crb/chunk",
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+ .version_id = 0,
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+ .needed = tpm_crb_chunk_needed,
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+ .post_load_errp = tpm_crb_chunk_post_load,
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+ .fields = (const VMStateField[]) {
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+ VMSTATE_GBYTEARRAY(command_buffer, CRBState, 0),
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+ VMSTATE_GBYTEARRAY(response_buffer, CRBState, 0),
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+ VMSTATE_UINT32(response_offset, CRBState),
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+ VMSTATE_END_OF_LIST()
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+ }
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+};
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+
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static const VMStateDescription vmstate_tpm_crb = {
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.name = "tpm-crb",
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.pre_save = tpm_crb_pre_save,
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.fields = (const VMStateField[]) {
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VMSTATE_UINT32_ARRAY(regs, CRBState, TPM_CRB_R_MAX),
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VMSTATE_END_OF_LIST(),
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+ },
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+ .subsections = (const VMStateDescription * const []) {
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+ &vmstate_tpm_crb_chunk,
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+ NULL,
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}
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};
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static const Property tpm_crb_properties[] = {
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DEFINE_PROP_TPMBE("tpmdev", CRBState, tpmbe),
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DEFINE_PROP_BOOL("cap-chunk", CRBState, cap_chunk, true),
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+ DEFINE_PROP_BOOL("x-allow-chunk-migration", CRBState,
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+ allow_chunk_migration, true),
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};
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static void tpm_crb_reset(void *dev)
@@ -415,6 +468,7 @@ static void tpm_crb_reset(void *dev)
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static void tpm_crb_realize(DeviceState *dev, Error **errp)
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{
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CRBState *s = CRB(dev);
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+ int ret;
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if (!tpm_find()) {
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error_setg(errp, "at most one TPM device is permitted");
@@ -424,6 +478,15 @@ static void tpm_crb_realize(DeviceState *dev, Error **errp)
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error_setg(errp, "'tpmdev' property is required");
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return;
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}
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+ if (s->cap_chunk && !s->allow_chunk_migration) {
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+ error_setg(&s->migration_blocker,
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+ "The tpm-crb device does not support chunk migration with "
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+ "machine version less than 11.1");
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+ ret = migrate_add_blocker_normal(&s->migration_blocker, errp);
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+ if (ret < 0) {
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+ return;
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+ }
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+ }
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memory_region_init_io(&s->mmio, OBJECT(s), &tpm_crb_memory_ops, s,
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"tpm-crb-mmio", sizeof(s->regs));
@@ -454,6 +517,10 @@ static void tpm_crb_unrealize(DeviceState *dev)
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g_clear_pointer(&s->command_buffer, g_byte_array_unref);
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g_clear_pointer(&s->response_buffer, g_byte_array_unref);
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+
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+ if (s->migration_blocker) {
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+ migrate_del_blocker(&s->migration_blocker);
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+ }
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}
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static void tpm_crb_class_init(ObjectClass *klass, const void *data)