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Date: Mon, 13 Sep 2021 12:29:13 +0200
From: Borislav Petkov <bp@alien8.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: nvdimm@lists.linux.dev, Jane Chu <jane.chu@oracle.com>,
	Luis Chamberlain <mcgrof@suse.com>, Tony Luck <tony.luck@intel.com>
Subject: Re: [RFT PATCH] x86/pat: Fix set_mce_nospec() for pmem
Message-ID: <YT8n+ae3lBQjqoDs@zn.tnic>
References: <162561960776.1149519.9267511644788011712.stgit@dwillia2-desk3.amr.corp.intel.com>
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In-Reply-To: <162561960776.1149519.9267511644788011712.stgit@dwillia2-desk3.amr.corp.intel.com>

On Tue, Jul 06, 2021 at 06:01:05PM -0700, Dan Williams wrote:
> When poison is discovered and triggers memory_failure() the physical
> page is unmapped from all process address space. However, it is not
> unmapped from kernel address space. Unlike a typical memory page that
> can be retired from use in the page allocator and marked 'not present',
> pmem needs to remain accessible given it can not be physically remapped
> or retired.

I'm surely missing something obvious but why does it need to remain
accessible? Spell it out please.

> set_memory_uc() tries to maintain consistent nominal memtype
> mappings for a given pfn, but memory_failure() is an exceptional
> condition.

That's not clear to me too. So looking at the failure:

[10683.426147] x86/PAT: fsdax_poison_v1:5018 conflicting memory types 1850600000-1850601000  uncached-minus<->write-back

set_memory_uc() marked it UC- but something? wants it to be WB. Why?

I guess I need some more info on the whole memory offlining for pmem and
why that should be done differently than with normal memory.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette