linux-kernel - Re: [PATCH] powerpc/mm: update arch_{add,remove}

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Date:	Wed, 29 Jun 2016 10:37:31 -0500
From:	Reza Arbab <arbab@...ux.vnet.ibm.com>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Balbir Singh <bsingharora@...il.com>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	David Gibson <david@...son.dropbear.id.au>,
	Vasant Hegde <hegdevasant@...ux.vnet.ibm.com>,
	Scott Wood <scottwood@...escale.com>,
	"Oliver O'Halloran" <oohall@...il.com>,
	Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/mm: update arch_{add,remove}_memory() for radix

On Tue, Jun 28, 2016 at 09:21:05PM +1000, Michael Ellerman wrote:
>No, you need to use mmu_linear_psize for the hotplug case.
>
>But you can probably factor out a common routine that both cases use, and hide
>the hash vs radix check in that.

Okay, I'm trying to refactor {create,remove}_section_mapping() into 
hash__ and radix__ variants. This lead to a couple of questions.

Pseudocode for radix__create_section_mapping(start, end):

	page_size = 1 << mmu_psize_defs[mmu_linear_psize].shift;
	start = _ALIGN_DOWN(start, page_size);

	for (; start < end; start += page_size) {
		radix__map_kernel_page(start, __pa(start),
				       PAGE_KERNEL, page_size);
	}

Should the above use PAGE_KERNEL, like the the hash table bolt, or 
(_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_KERNEL_RW), like in the radix 
vmemmap creation?

The other question is what radix__remove_section_mapping() should do.
I don't know offhand what the opposite of map_kernel_page() is. As 
Aneesh mentioned, radix vmemmap removal is currently stubbed as a FIXME 
so I couldn't use that as a reference.

-- 
Reza Arbab