Re: [PATCH v4] ppc/fadump: collect dump when CPU_STATE_DATA is less than reserved

[Anushree Mathur <anushree.mathur2@ibm.com>]

On 28/08/26 3:19 PM, 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 <anushree.mathur@linux.vnet.ibm.com>
> Closes: https://lore.kernel.org/all/5e66daf4-3f55-4044-94a5-4f50bb040849@linux.ibm.com/T/#u
> Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
> ---
>
> Changelog:
> v4:
>      removed extra blank line.
>
> v3: https://lore.kernel.org/all/20260827075803.2240934-1-shivangu@linux.ibm.com/
>      removed extra variable.
>
> v2: https://lore.kernel.org/all/20260826125626.2108771-1-shivangu@linux.ibm.com/
>      Only allowing lesser size for CPU_STATE_DATE Fadump region.
>
> v1: https://lore.kernel.org/qemu-devel/20260429065127.366813-1-shivangu@linux.ibm.com/
>
> ---
>   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))) {
> +
>   				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;
>   			}
> +
>   			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;

Hi Shivang,
Thanks for working on this fix, I have tested it with patched kernel on 
both PowerVM (ppc64le) lpar and guest, and it worked totally fine.

As reported earlier 
https://lore.kernel.org/lkml/5e66daf4-3f55-4044-94a5-4f50bb040849@linux.ibm.com/ 
without patch I was seeing multiple kernel OOPS and

     [    0.045806] [      T1] rtas fadump: Dump taken by platform is
         incomplete (0)

After applying the patch I am not seeing OOPS and not even this error :
"[    0.045806] [      T1] rtas fadump: Dump taken by platform is incomplete (0)"

Fadump got completed and I came back to guest console successfully.

Please feel free to add:

Tested-by: Anushree Mathur<anushree.mathur@linux.ibm.com>
Thank you,
Anushree Mathur