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

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Date: Fri, 21 Jun 2024 16:27:44 -0400
From: Peter Xu <peterx@...hat.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Hansen, Dave" <dave.hansen@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hughd@...gle.com" <hughd@...gle.com>,
	"willy@...radead.org" <willy@...radead.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"vbabka@...e.cz" <vbabka@...e.cz>,
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	"kirill@...temov.name" <kirill@...temov.name>,
	"christophe.leroy@...roup.eu" <christophe.leroy@...roup.eu>,
	"Jiang, Dave" <dave.jiang@...el.com>,
	"aneesh.kumar@...ux.ibm.com" <aneesh.kumar@...ux.ibm.com>,
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	"Huang, Ying" <ying.huang@...el.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH 6/7] mm/x86: Add missing pud helpers

On Fri, Jun 21, 2024 at 07:36:30PM +0000, Edgecombe, Rick P wrote:
> On Fri, 2024-06-21 at 07:51 -0700, Dave Hansen wrote:
> > 
> > But, still, what if you take a Dirty=1,Write=1 pud and pud_modify() it
> > to make it Dirty=1,Write=0?  What prevents that from being
> > misinterpreted by the hardware as being a valid 1G shadow stack mapping?
> 
> Hmm, it looks like we could use an arch_check_zapped_pud() that does a warning
> like arch_check_zapped_pte/pmd() too. Not that we had no use for one before
> this.

I can definitely look into that, but this check only happens when zapping,
and IIUC it means there can still be outliers floating around.  I wonder
whether it should rely on page_table_check_pxx_set() from that regard.

Thanks,

-- 
Peter Xu