linux-kernel - Re: uninitialized pmem struct pages

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Message-ID: <bf26f568-79b3-67f9-832a-9d8ef3f72c43@redhat.com>
Date:   Mon, 4 Jan 2021 16:43:49 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Dan Williams <dan.j.williams@...el.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: uninitialized pmem struct pages

On 04.01.21 16:33, Michal Hocko wrote:
> On Mon 04-01-21 16:15:23, David Hildenbrand wrote:
>> On 04.01.21 16:10, Michal Hocko wrote:
> [...]
>> Do the physical addresses you see fall into the same section as boot
>> memory? Or what's around these addresses?
> 
> Yes I am getting a garbage for the first struct page belonging to the
> pmem section [1]
> [    0.020161] ACPI: SRAT: Node 0 PXM 0 [mem 0x100000000-0x603fffffff]
> [    0.020163] ACPI: SRAT: Node 4 PXM 4 [mem 0x6060000000-0x11d5fffffff] non-volatile
> 
> The pfn without the initialized struct page is 0x6060000. This is a
> first pfn in a section.

Okay, so we're not dealing with the "early section" mess I described,
different story.

Due to [1], is_mem_section_removable() called
pfn_to_page(PHYS_PFN(0x6060000)). page_zone(page) made it crash, as not
initialized.

Let's assume this is indeed a reserved pfn in the altmap. What's the
actual address of the memmap?

I do wonder what hosts pfn_to_page(PHYS_PFN(0x6060000)) - is it actually
part of the actual altmap (i.e. > 0x6060000) or maybe even self-hosted?

If it's not self-hosted, initializing the relevant memmaps should work
just fine I guess. Otherwise things get more complicated.

-- 
Thanks,

David / dhildenb