linux-kernel - Re: [PATCH 6/7] mm/x86: Add missing pud helpers

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Message-ID: <ZnhCX-GMRn_uYDF8@x1n>
Date: Sun, 23 Jun 2024 11:42:23 -0400
From: Peter Xu <peterx@...hat.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>, Dave Jiang <dave.jiang@...el.com>,
	"Kirill A . Shutemov" <kirill@...temov.name>,
	Ingo Molnar <mingo@...hat.com>, Oscar Salvador <osalvador@...e.de>,
	Matthew Wilcox <willy@...radead.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Dan Williams <dan.j.williams@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>, linuxppc-dev@...ts.ozlabs.org,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Rik van Riel <riel@...riel.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
	Nicholas Piggin <npiggin@...il.com>,
	Huang Ying <ying.huang@...el.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH 6/7] mm/x86: Add missing pud helpers

On Fri, Jun 21, 2024 at 09:11:56AM -0700, Dave Hansen wrote:
> It's in the "Determination of Access Rights" section.
> 
> 	A linear address is a shadow-stack address if the following are
> 	true of the translation of the linear address: (1) the R/W flag
> 	(bit 1) is 0 and the dirty flag (bit 6) is 1 in the paging-
> 	structure entry that maps the page containing the linear
> 	address; and (2) the R/W flag is 1 in every other paging-
> 	structure entry controlling the translation of the linear
> 	address.

Thanks.  It'll be nice if this can be referenced in the pgtable definitions
too in some way.

[...]

> One big thing I did in this review was make sure that the PMD and PUD
> helpers were doing the same thing.  Would you mind circling back and
> double-checking the same before you repost this?

Sure, I'll make sure I'll at least add a comment if it doesn't match and
explain why.  I actually did it already e.g. in the _modify path for shadow
stack, but I failed this spot.

The page table check thing is really rare that I overlooked, could be
relevant to what I used to hit a bug but fixed around this area, so I
forgot to add it back, but I really can't remember. I'll keep an extra eye
on that.

Thanks,

-- 
Peter Xu