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Message-ID: <b78bc160a361a25ac0e6ca8ca8a3dfb376a140b1.camel@intel.com>
Date: Tue, 31 Aug 2021 18:48:47 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "rppt@...nel.org" <rppt@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"peterz@...radead.org" <peterz@...radead.org>, "keescook@...omium.org"
<keescook@...omium.org>, "Weiny, Ira" <ira.weiny@...el.com>,
"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>, "vbabka@...e.cz" <vbabka@...e.cz>,
"x86@...nel.org" <x86@...nel.org>, "akpm@...ux-foundation.org"
<akpm@...ux-foundation.org>, "Williams, Dan J" <dan.j.williams@...el.com>,
"Lutomirski, Andy" <luto@...nel.org>, "kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>, "Hansen, Dave"
<dave.hansen@...el.com>, "shakeelb@...gle.com" <shakeelb@...gle.com>
Subject: Re: [RFC PATCH v2 10/19] x86/mm: Use alloc_table() for fill_pte(),
etc
On Tue, 2021-08-31 at 11:47 +0300, Mike Rapoport wrote:
> On Mon, Aug 30, 2021 at 04:59:18PM -0700, Rick Edgecombe wrote:
> > fill_pte(), set_pte_vaddr(), etc allocate page tables with
> > spp_getpage(). Use alloc_table() for these allocations in order to
> > get
> > tables from the cache of protected pages when needed.
>
>
> I can't say I tracked all the users of set_pte_vaddr(), but I don't
> see a
> fundamental reason why spp_getpage() would need GFP_ATOMIC.
Yea, I couldn't find why it was done that way in the first place, and
there were almost too many callers to audit. I guess I could roll up my
sleeves an audit it all, but its not foolproof. Or put a warn for
atomic context and pull all of the GFP_ATOMIC code if it doesn't get
triggered after awhile. Also seems weird that it just panics here if
the allocation fails.
> Even if there
> is a caller of set_pte_vaddr() that cannot sleep, it seems that page
> tables
> can be prepopulated so that set_pte_vaddr() will not need to allocate
> anything.
Hmm, could work for the fixmap callers I guess (maybe already happening
in practice). Xen and a few other things seems to use this for non-
fixmap things, but it's during init and easier to audit.
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