Hello Michael,


On 22/11/23 10:47, Michael Ellerman wrote:

Aneesh Kumar K V [off-list ref] writes:
...

quoted

I am not sure whether we need to add all the complexity to enable supporting different fadump kernel
version. Is that even a possible use case with fadump? Can't we always assume that with fadump the
crash kernel and fadump kernel will be same version?

How sure are we of that?

Don't we go through grub when we boot into the 2nd kernel. And so
couldn't it choose to boot a different kernel, for whatever reason.

I don't think we need to support different pt_reg / cpumask sizes, but
requiring the exact same kernel version is too strict I think.

Agree.

But maybe I'm wrong. Would be good to hear what distro folks think.

How about checking fadump crash info header compatibility in the 
following way?

static bool is_fadump_header_compatible(struct fadump_crash_info_header 
*fdh)
{
     if (fdh->magic_number == FADUMP_CRASH_INFO_MAGIC_OLD) {
         pr_err("Old magic number, can't process the dump.");
         return false;
     }

     if (fdh->magic_number != FADUMP_CRASH_INFO_MAGIC) {
         pr_err("Fadump header is corrupted.");
         return false;
     }

     /*
      * If the kernel version of the first/crashed kernel and the 
second/fadump
      * kernel is not same, then only collect the dump if the size of all
      * non-primitive type members of the fadump header is the same 
across kernels.
      */
     if (strcmp(fdh->kernel_version, init_uts_ns.name.release)) {
         if (fdh->pt_regs_sz != sizeof(struct pt_regs) || 
fdh->cpu_mask_sz != sizeof(struct cpumask)) {
             pr_err("Fadump header size mismatch.\n")
             return false;
         } else
             pr_warn("Kernel version mismatch; dump data is unreliable.\n");
     }

     return true;
}

And the new fadump crash info header will be: As suggested by Hari.

/* fadump crash info structure */
struct fadump_crash_info_header {
     u64        magic_number;
+  u32        version;
     u32        crashing_cpu;
     u64        elfcorehdr_addr;
+  u64        elfcorehdr_size;
+  u64        vmcoreinfo_raddr;
+  u64        vmcoreinfo_size;
+  u8          kernel_version[__NEW_UTS_LEN + 1];
+  u32        pt_regs_sz;
     struct pt_regs    regs;
+  u32        cpu_mask_sz;
     struct cpumask    cpu_mask;
};

Thanks,
Sourabh Jain