Re: [PATCH v4 6/8] hw/ppc: Pass dump-sizes property for fadump in device tree

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 23/03/25 23:10, Aditya Gupta wrote:
> Platform (ie. QEMU) is expected to pass few device tree properties for
> details for fadump:
>
>    * "ibm,configure-kernel-dump-sizes": Space required to store dump data
>      for firmware provided dump sections (ie. CPU & HPTE regions)
>    * "ibm,configure-kernel-dump-version": Versions of fadump supported
>
> Pass the above device tree nodes so that kernel can reserve sufficient
> space for preserving the CPU state data
>
> Note: As of this patch, the "kernel-dump" device tree entry is still not
> added for the second boot, so after crash, the second kernel will boot
> assuming fadump dump is "NOT" active, and try to register for fadump,
> but since we already have fadump registered in QEMU internal state, the
> register rtas call will fail with: "DUMP ACTIVE"
>
> Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
> ---
>   hw/ppc/spapr.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 57 insertions(+)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index a415e51d077a..3cbc6a7409b7 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -900,6 +900,61 @@ static int spapr_dt_rng(void *fdt)
>       return ret ? -1 : 0;
>   }
>   
> +static void spapr_dt_rtas_fadump(SpaprMachineState *spapr, void *fdt, int rtas)
> +{
> +    MachineState *ms = MACHINE(spapr);
> +    MachineClass *mc = MACHINE_GET_CLASS(ms);
> +
> +    uint32_t max_possible_cpus = mc->possible_cpu_arch_ids(ms)->len;
> +    uint64_t fadump_cpu_state_size = 0;
> +    uint16_t fadump_versions[2] = {
> +        FADUMP_VERSION /* min supported version */,
> +        FADUMP_VERSION /* max supported version */
> +    };
> +    uint32_t fadump_rgn_sizes[2][3] = {
> +        {
> +            cpu_to_be32(FADUMP_CPU_STATE_DATA),
> +            0, 0 /* Calculated later */
> +        },
> +        {
> +            cpu_to_be32(FADUMP_HPTE_REGION),
> +            0, 0 /* HPTE region not implemented */
> +        }

#nit-pick
Why to advertise if we don't support it? Kernel anyways ignores this for 
now.

> +    };
> +
> +    /*
> +     * CPU State Data contains multiple fields such as header, num_cpus and
> +     * register entries
> +     *
> +     * Calculate the maximum CPU State Data size, according to maximum
> +     * possible CPUs the QEMU VM can have
> +     *
> +     * This calculation must match the 'cpu_state_len' calculation done in
> +     * 'populate_cpu_state_data' in spapr_fadump.c
> +     */
> +    fadump_cpu_state_size += sizeof(struct FadumpRegSaveAreaHeader);
> +    fadump_cpu_state_size += 0xc;                      /* padding as in PAPR */
> +    fadump_cpu_state_size += sizeof(__be32);           /* num_cpus */
> +    fadump_cpu_state_size += max_possible_cpus   *     /* reg entries */
> +                             FADUMP_NUM_PER_CPU_REGS *
> +                             sizeof(struct FadumpRegEntry);
> +
> +    /* Set maximum size for CPU state data region */
> +    assert(fadump_rgn_sizes[0][0] == cpu_to_be32(FADUMP_CPU_STATE_DATA));
> +
> +    /* Upper 32 bits of size, usually 0 */
> +    fadump_rgn_sizes[0][1] = cpu_to_be32(fadump_cpu_state_size >> 32);
> +
> +    /* Lower 32 bits of size */
> +    fadump_rgn_sizes[0][2] = cpu_to_be32(fadump_cpu_state_size & 0xffffffff);
> +
> +    /* Add device tree properties required from platform for fadump */
> +    _FDT((fdt_setprop(fdt, rtas, "ibm,configure-kernel-dump-version",
> +                    fadump_versions, sizeof(fadump_versions))));
> +    _FDT((fdt_setprop(fdt, rtas, "ibm,configure-kernel-dump-sizes",
> +                    fadump_rgn_sizes, sizeof(fadump_rgn_sizes))));
> +}
> +
>   static void spapr_dt_rtas(SpaprMachineState *spapr, void *fdt)
>   {
>       MachineState *ms = MACHINE(spapr);
> @@ -1012,6 +1067,8 @@ static void spapr_dt_rtas(SpaprMachineState *spapr, void *fdt)
>       _FDT(fdt_setprop(fdt, rtas, "ibm,lrdr-capacity",
>                        lrdr_capacity, sizeof(lrdr_capacity)));
>   
> +    spapr_dt_rtas_fadump(spapr, fdt, rtas);
> +
>       spapr_dt_rtas_tokens(fdt, rtas);
>   }
>