Re: [PATCH 3/3] backends/tpm: Propagate vTPM error on migration failure

[Stefan Berger <stefanb@linux.ibm.com>]

On 6/24/25 8:23 AM, Arun Menon wrote:
> - Introduce a new post_load_with_error() hook that will
>    take in the Error object as a parameter.
> - This error object is set if the loading of state fails.
> - The error can then be retrieved using QMP command
>    {"execute" : "query-migrate"}
> 
> Buglink: https://issues.redhat.com/browse/RHEL-82826
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>

> ---
>   backends/tpm/tpm_emulator.c | 39 ++++++++++++++++++++-------------------
>   include/migration/vmstate.h |  1 +
>   migration/vmstate.c         |  4 +++-
>   3 files changed, 24 insertions(+), 20 deletions(-)
> 
> diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c
> index 4a234ab2c0b19b2604bf0dd8cb5f4540c72a9438..816134d7b4de00a75a3d0b928d160595b17be810 100644
> --- a/backends/tpm/tpm_emulator.c
> +++ b/backends/tpm/tpm_emulator.c
> @@ -819,7 +819,8 @@ static int tpm_emulator_get_state_blobs(TPMEmulator *tpm_emu)
>   static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>                                          uint32_t type,
>                                          TPMSizedBuffer *tsb,
> -                                       uint32_t flags)
> +                                       uint32_t flags,
> +                                       Error **errp)
>   {
>       ssize_t n;
>       ptm_setstate pss;
> @@ -838,17 +839,17 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>       /* write the header only */
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_STATEBLOB, &pss,
>                                offsetof(ptm_setstate, u.req.data), 0, 0) < 0) {
> -        error_report("tpm-emulator: could not set state blob type %d : %s",
> -                     type, strerror(errno));
> +        error_setg(errp, "tpm-emulator: could not set state blob type %d : %s",
> +                   type, strerror(errno));
>           return -1;
>       }
> 
>       /* now the body */
>       n = qemu_chr_fe_write_all(&tpm_emu->ctrl_chr, tsb->buffer, tsb->size);
>       if (n != tsb->size) {
> -        error_report("tpm-emulator: Writing the stateblob (type %d) "
> -                     "failed; could not write %u bytes, but only %zd",
> -                     type, tsb->size, n);
> +        error_setg(errp, "tpm-emulator: Writing the stateblob (type %d) "
> +                   "failed; could not write %u bytes, but only %zd",
> +                   type, tsb->size, n);
>           return -1;
>       }
> 
> @@ -856,17 +857,17 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>       n = qemu_chr_fe_read_all(&tpm_emu->ctrl_chr,
>                                (uint8_t *)&pss, sizeof(pss.u.resp));
>       if (n != sizeof(pss.u.resp)) {
> -        error_report("tpm-emulator: Reading response from writing stateblob "
> -                     "(type %d) failed; expected %zu bytes, got %zd", type,
> -                     sizeof(pss.u.resp), n);
> +        error_setg(errp, "tpm-emulator: Reading response from writing "
> +                   "stateblob (type %d) failed; expected %zu bytes, "
> +                   "got %zd", type, sizeof(pss.u.resp), n);
>           return -1;
>       }
> 
>       tpm_result = be32_to_cpu(pss.u.resp.tpm_result);
>       if (tpm_result != 0) {
> -        error_report("tpm-emulator: Setting the stateblob (type %d) failed "
> -                     "with a TPM error 0x%x %s", type, tpm_result,
> -                     tpm_emulator_strerror(tpm_result));
> +        error_setg(errp, "tpm-emulator: Setting the stateblob (type %d) "
> +                   "failed with a TPM error 0x%x %s", type, tpm_result,
> +                   tpm_emulator_strerror(tpm_result));
>           return -1;
>       }
> 
> @@ -880,7 +881,7 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>    *
>    * Returns a negative errno code in case of error.
>    */
> -static int tpm_emulator_set_state_blobs(TPMBackend *tb)
> +static int tpm_emulator_set_state_blobs(TPMBackend *tb, Error **errp)
>   {
>       TPMEmulator *tpm_emu = TPM_EMULATOR(tb);
>       TPMBlobBuffers *state_blobs = &tpm_emu->state_blobs;
> @@ -894,13 +895,13 @@ static int tpm_emulator_set_state_blobs(TPMBackend *tb)
> 
>       if (tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_PERMANENT,
>                                       &state_blobs->permanent,
> -                                    state_blobs->permanent_flags) < 0 ||
> +                                    state_blobs->permanent_flags, errp) < 0 ||
>           tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_VOLATILE,
>                                       &state_blobs->volatil,
> -                                    state_blobs->volatil_flags) < 0 ||
> +                                    state_blobs->volatil_flags, errp) < 0 ||
>           tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_SAVESTATE,
>                                       &state_blobs->savestate,
> -                                    state_blobs->savestate_flags) < 0) {
> +                                    state_blobs->savestate_flags, errp) < 0) {
>           return -EIO;
>       }
> 
> @@ -948,12 +949,12 @@ static void tpm_emulator_vm_state_change(void *opaque, bool running,
>    *
>    * Returns negative errno codes in case of error.
>    */
> -static int tpm_emulator_post_load(void *opaque, int version_id)
> +static int tpm_emulator_post_load(void *opaque, int version_id, Error **errp)
>   {
>       TPMBackend *tb = opaque;
>       int ret;
> 
> -    ret = tpm_emulator_set_state_blobs(tb);
> +    ret = tpm_emulator_set_state_blobs(tb, errp);
>       if (ret < 0) {
>           return ret;
>       }
> @@ -969,7 +970,7 @@ static const VMStateDescription vmstate_tpm_emulator = {
>       .name = "tpm-emulator",
>       .version_id = 0,
>       .pre_save = tpm_emulator_pre_save,
> -    .post_load = tpm_emulator_post_load,
> +    .post_load_with_error = tpm_emulator_post_load,
>       .fields = (const VMStateField[]) {
>           VMSTATE_UINT32(state_blobs.permanent_flags, TPMEmulator),
>           VMSTATE_UINT32(state_blobs.permanent.size, TPMEmulator),
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index 056781b1c21e737583f081594d9f88b32adfd674..1c6e89c3b08a3914cde6dce3be5955978b6b7d0b 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -207,6 +207,7 @@ struct VMStateDescription {
>       MigrationPriority priority;
>       int (*pre_load)(void *opaque);
>       int (*post_load)(void *opaque, int version_id);
> +    int (*post_load_with_error)(void *opaque, int version_id, Error **errp);
>       int (*pre_save)(void *opaque);
>       int (*post_save)(void *opaque);
>       bool (*needed)(void *opaque);
> diff --git a/migration/vmstate.c b/migration/vmstate.c
> index 3f8c3d3c1dcfe14d70bab1f43b827244eb4bb385..c5dfffd9bad7285e819d4769e055d47157caab34 100644
> --- a/migration/vmstate.c
> +++ b/migration/vmstate.c
> @@ -232,7 +232,9 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
>           qemu_file_set_error(f, ret);
>           return ret;
>       }
> -    if (vmsd->post_load) {
> +    if (vmsd->post_load_with_error) {
> +        ret = vmsd->post_load_with_error(opaque, version_id, errp);
> +    } else if (vmsd->post_load) {
>           ret = vmsd->post_load(opaque, version_id);
>       }
>       trace_vmstate_load_state_end(vmsd->name, "end", ret);
>