Re: [PATCH v2 08/39] x86/mm: Remove _PAGE_DIRTY from kernel RO pages

From: Andrew Cooper
Date: Tue Oct 04 2022 - 21:32:15 EST

On 29/09/2022 23:29, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Processors sometimes directly create Write=0,Dirty=1 PTEs.

Do they? (Rhetorical)

Yes, this is a relevant anecdote for why CET isn't available on pre-TGL
parts, but it one of the more wrong things to have as the first sentence
of this commit message.

The point you want to express is that under the CET-SS spec, R/O+Dirty
has a new meaning as type=shstk, so stop using this bit combination for
existing mappings.

I'm not even sure it's relevant to note that CET capable processors can
set D on a R/O mapping, because that depends on !CR0.WP which in turn
prohibits CR4.CET being enabled.