[PATCH v3 0/4] powerpc/mm/radix: Memory unplug fixes

[Michael Ellerman]

Nathan Lynch <nathanl at linux.ibm.com> writes:
> "Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com> writes:
>> This is the next version of the fixes for memory unplug on radix.
>> The issues and the fix are described in the actual patches.
>
> I guess this isn't actually causing problems at runtime right now, but I
> notice calls to resize_hpt_for_hotplug() from arch_add_memory() and
> arch_remove_memory(), which ought to be mmu-agnostic:
>
> int __ref arch_add_memory(int nid, u64 start, u64 size,
> 			  struct mhp_params *params)
> {
> 	unsigned long start_pfn = start >> PAGE_SHIFT;
> 	unsigned long nr_pages = size >> PAGE_SHIFT;
> 	int rc;
>
> 	resize_hpt_for_hotplug(memblock_phys_mem_size());
>
> 	start = (unsigned long)__va(start);
> 	rc = create_section_mapping(start, start + size, nid,
> 				    params->pgprot);
> ...

Hmm well spotted.

That does return early if the ops are not setup:

int resize_hpt_for_hotplug(unsigned long new_mem_size)
{
	unsigned target_hpt_shift;

	if (!mmu_hash_ops.resize_hpt)
		return 0;


And:

void __init hpte_init_pseries(void)
{
	...
	if (firmware_has_feature(FW_FEATURE_HPT_RESIZE))
		mmu_hash_ops.resize_hpt = pseries_lpar_resize_hpt;

And that comes in via ibm,hypertas-functions:

	{FW_FEATURE_HPT_RESIZE,		"hcall-hpt-resize"},


But firmware is not necessarily going to add/remove that call based on
whether we're using hash/radix.

So I think a follow-up patch is needed to make this more robust.

Aneesh/Bharata what platform did you test this series on? I'm curious
how this didn't break.

cheers