linux-kernel - Re: [PATCH 05/21] x86/mm/pat: mirror direct map changes to ASI

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Message-ID: <DFU8STXKQXN9.E9NXUMU72SFQ@google.com>
Date: Wed, 21 Jan 2026 11:49:13 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Borislav Petkov <bp@...en8.de>, Brendan Jackman <jackmanb@...gle.com>
Cc: Dave Hansen <dave.hansen@...el.com>, Andy Lutomirski <luto@...nel.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, 
	Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>, 
	Axel Rasmussen <axelrasmussen@...gle.com>, Yuanchu Xie <yuanchu@...gle.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, <peterz@...radead.org>, 
	<dave.hansen@...ux.intel.com>, <mingo@...hat.com>, <tglx@...utronix.de>, 
	<akpm@...ux-foundation.org>, <david@...hat.com>, <derkling@...gle.com>, 
	<junaids@...gle.com>, <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, 
	<reijiw@...gle.com>, <rientjes@...gle.com>, <rppt@...nel.org>, 
	<vbabka@...e.cz>, <x86@...nel.org>, Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH 05/21] x86/mm/pat: mirror direct map changes to ASI

On Wed Jan 21, 2026 at 11:27 AM UTC, Borislav Petkov wrote:
> On Wed, Jan 21, 2026 at 09:45:22AM +0000, Brendan Jackman wrote:
>> 2. The property of some memory being mapped or unmapped in the
>>    "restricted"/"partial"/"sensitive" address space (current patch's
>>    terminology: sensitive/nonsensitive).
>
> Why do we care about the sensitivity of memory? To the kernel it doesn't
> matter whether memory is sensitive or not. You simply map it in the sensitive
> page table or in the nonsensitive or in both.
>
> Having a sensitive and nonsensitive pagetable should be enough. And that'll
> make the whole concept a lot simpler.

Well, something has to manage those pagetables and that thing needs a
term to describe the stuff it's acting on. I.e. we need an adjective
better than "to-be-mapped-into-the-full-pagtable".

Anyway, I think this will be an easier debate to have once we're looking
at actual code etc - I'm still debugging my page allocator changes to
support the guest_memfd thing and that code doesn't need to care about
"sensitivity" at all, there's just one address space and data is
"mapped" or "unmapped". So I propose we defer this conversation until
after that...