On Fri, Aug 28, 2026 at 03:19:42PM +0530, Shivang Upadhyay wrote:
> During Fadump in Qemu VM, when maxcpus value is set to more than current
> cpus, following failure is observed.
>
> [ 0.045806] [ T1] rtas fadump: Dump taken by platform is
> incomplete (0)
>
> This is because the CPU_STATE_DATA is allocated for maxcpus, while the
> data is only filled for current cpus. As per current implementation
> of Fadump, dumped_bytes and source_len for a region have to match,
> Which is failing for qemu's case, Even tough the dumped bytes are
> reported correctly for only the current cpus. After this /proc/vmcore
> generatition also fails.
>
> Allowing dumped_bytes to be lesser than or equal to allocated length, for
> CPU_STATE_DATA Fadump region.
>
> Reported-by: Anushree Mathur <[email protected]>
> Closes:
> https://lore.kernel.org/all/[email protected]/T/#u
> Signed-off-by: Shivang Upadhyay <[email protected]>
> ---
>
> Changelog:
> v4:
> removed extra blank line.
>
> v3:
> https://lore.kernel.org/all/[email protected]/
> removed extra variable.
>
> v2:
> https://lore.kernel.org/all/[email protected]/
> Only allowing lesser size for CPU_STATE_DATE Fadump region.
>
> v1:
> https://lore.kernel.org/qemu-devel/[email protected]/
>
> ---
> arch/powerpc/platforms/pseries/rtas-fadump.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/rtas-fadump.c
> b/arch/powerpc/platforms/pseries/rtas-fadump.c
> index 3bb4ac2ab6cc..838e97c24308 100644
> --- a/arch/powerpc/platforms/pseries/rtas-fadump.c
> +++ b/arch/powerpc/platforms/pseries/rtas-fadump.c
> @@ -459,6 +459,8 @@ static int __init rtas_fadump_process(struct fw_dump
> *fadump_conf)
> /* Check if the dump data is valid. */
> for (int i = 0; i < be16_to_cpu(fdm_active->header.dump_num_sections);
> i++) {
> int type = be16_to_cpu(fdm_active->rgn[i].source_data_type);
> + uint64_t bytes_dumped =
> be64_to_cpu(fdm_active->rgn[i].bytes_dumped);
> + uint64_t source_len =
> be64_to_cpu(fdm_active->rgn[i].source_len);
> int rc = 0;
>
> switch (type) {
> @@ -469,10 +471,20 @@ static int __init rtas_fadump_process(struct fw_dump
> *fadump_conf)
> pr_err("Dump taken by platform is not valid
> (%d)\n", i);
> rc = -EINVAL;
> }
> - if (fdm_active->rgn[i].bytes_dumped !=
> fdm_active->rgn[i].source_len) {
> +
> + /*
> + * Make sure that dump is collected for entire region.
> + * CPU_STATE_DATA region is allowed to dump less than
> allocated space.
> + */
> + if (!(bytes_dumped == source_len ||
> + (type == RTAS_FADUMP_CPU_STATE_DATA && bytes_dumped <=
> source_len))) {
> +
Extra line here.
> pr_err("Dump taken by platform is incomplete
> (%d)\n", i);
> + pr_debug("type -> %d, bytes_dumped -> %llx,
> source_len -> %llx\n",
> + type, bytes_dumped, source_len);
> rc = -EINVAL;
> }
Can bytes_dumped be greater than source_len?
If yes then the error is misinformed that it's incomplete instead it's
corrupted.
If No then shouldn't the internal check bytes_dumped <= source_len should
handle it?
Regards,
Mukesh
> +
> if (rc) {
> pr_warn("Region type: %u src addr: 0x%llx dest
> addr: 0x%llx\n",
>
> be16_to_cpu(fdm_active->rgn[i].source_data_type),
> @@ -482,7 +494,7 @@ static int __init rtas_fadump_process(struct fw_dump
> *fadump_conf)
> }
> break;
> case RTAS_FADUMP_PARAM_AREA:
> - if (fdm_active->rgn[i].bytes_dumped !=
> fdm_active->rgn[i].source_len ||
> + if (bytes_dumped != source_len ||
> fdm_active->rgn[i].error_flags != 0) {
> pr_warn("Failed to process additional
> parameters! Proceeding anyway..\n");
> fadump_conf->param_area = 0;
> --
> 2.54.0
>
