powerpc/vmcore: Add MMU information to vmcoreinfo

Since below commit, address mapping for vmemmap has changed for Radix
MMU, where address mapping is stored in kernel page table itself,
instead of earlier used 'vmemmap_list'.

    commit 368a059 ("powerpc/book3s64/vmemmap: switch radix to use
    a different vmemmap handling function")

Hence with upstream kernel, in case of Radix MMU, makedumpfile fails
to do address translation for vmemmap addresses, as it depended on
vmemmap_list, which can now be empty.

While fixing the address translation in makedumpfile, it was identified
that currently makedumpfile cannot distinguish between Hash MMU and
Radix MMU, unless VMLINUX is passed with -x flag to makedumpfile. And
hence fails to assign offsets and shifts correctly (such as in L4 to
PGDIR offset calculation in makedumpfile).

For getting the MMU, makedumpfile uses `cur_cpu_spec.mmu_features`.

Add `cur_cpu_spec` symbol and offset of `mmu_features` in the `cpu_spec`
struct, to VMCOREINFO, so that makedumpfile can assign the offsets
correctly, without needing a VMLINUX.

Also, even along with `cur_cpu_spec->mmu_features` makedumpfile has to
depend on the 'MMU_FTR_TYPE_RADIX' flag in mmu_features, implying kernel
developers need to be cautious of changes to 'MMU_FTR_*' defines.

A more stable approach was suggested in the below thread by contributors:
 https://lore.kernel.org/linuxppc-dev/[email protected]/

The suggestion was to add whether 'RADIX_MMU' is enabled in vmcoreinfo

This patch also implements the suggestion, by adding 'RADIX_MMU' in
vmcoreinfo, which makedumpfile can use to get whether the crashed system
had RADIX MMU (in which case 'NUMBER(RADIX_MMU)=1') or not (in which
case 'NUMBER(RADIX_MMU)=0')

Fixes: 368a059 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function")
Reported-by: Sachin Sant <[email protected]>
Signed-off-by: Aditya Gupta <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

arch/powerpc/kexec/core.c

@@ -74,6 +74,9 @@ void arch_crash_save_vmcoreinfo(void)
 	VMCOREINFO_STRUCT_SIZE(mmu_psize_def);
 	VMCOREINFO_OFFSET(mmu_psize_def, shift);
 #endif
+	VMCOREINFO_SYMBOL(cur_cpu_spec);
+	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
+	vmcoreinfo_append_str("NUMBER(RADIX_MMU)=%d\n", early_radix_enabled());
 	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
 }