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From: Mike Rapoport <rppt@linux.ibm.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"keescook@chromium.org" <keescook@chromium.org>,
	"rppt@kernel.org" <rppt@kernel.org>,
	"Weiny, Ira" <ira.weiny@intel.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"vbabka@suse.cz" <vbabka@suse.cz>,
	"x86@kernel.org" <x86@kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"Lutomirski, Andy" <luto@kernel.org>
Subject: Re: [RFC PATCH 3/4] mm/page_alloc: introduce __GFP_PTE_MAPPED flag to allocate pte-mapped pages
Date: Tue, 24 Aug 2021 20:37:41 +0300	[thread overview]
Message-ID: <YSUuZfUAub6wvG9L@linux.ibm.com> (raw)
In-Reply-To: <c7ae898069360aff581be5eebeb74c0d03bb3bde.camel@intel.com>

On Tue, Aug 24, 2021 at 05:23:04PM +0000, Edgecombe, Rick P wrote:
> On Tue, 2021-08-24 at 19:54 +0300, Mike Rapoport wrote:
> > On Tue, Aug 24, 2021 at 04:38:03PM +0000, Edgecombe, Rick P wrote:
> > > On Tue, 2021-08-24 at 16:02 +0300, Mike Rapoport wrote:
> > > > > We probably want to exclude GFP_ATOMIC before calling into CPA
> > > > > unless
> > > > > debug page alloc is on, because it may need to split and sleep
> > > > > for
> > > > > the
> > > > > allocation. There is a page table allocation with GFP_ATOMIC
> > > > > passed
> > > > > actually.
> > > > 
> > > > Looking at the callers of alloc_low_pages() it seems that
> > > > GFP_ATOMIC
> > > > there
> > > > is stale...
> > > 
> > > Well two actually, there is also spp_getpage(). I tried to
> > > determine if
> > > that was also stale but wasn't confident. There were a lot of paths
> > > in.
> > 
> >   
> > It's also used at init and during memory hotplug, so I really doubt
> > it
> > needs GFP_ATOMIC.
> 
> Pretty sure it gets called after init by at least something besides
> hotplug. I saw it during debugging with a little sanitizer I built to
> find any unprotected page tables missed. Something tweaking the fixmap
> IIRC. Did you look at the set_fixmap_() and set_pte_vaddr() family of
> functions? Now whether any of them actually need GFP_ATOMIC, I am less
> sure. There were a fair amount of drivers to analyze.

Oh, I've missed set_pte_vaddr(). I still doubt anything that uses those two
would need GFP_ATOMIC, but it's surely way harder to analyze.

-- 
Sincerely yours,
Mike.

  reply	other threads:[~2021-08-24 17:41 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23 13:25 [RFC PATCH 0/4] mm/page_alloc: cache pte-mapped allocations Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 1/4] list: Support getting most recent element in list_lru Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 2/4] list: Support list head not in object for list_lru Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 3/4] mm/page_alloc: introduce __GFP_PTE_MAPPED flag to allocate pte-mapped pages Mike Rapoport
2021-08-23 20:29   ` Edgecombe, Rick P
2021-08-24 13:02     ` Mike Rapoport
2021-08-24 16:38       ` Edgecombe, Rick P
2021-08-24 16:54         ` Mike Rapoport
2021-08-24 17:23           ` Edgecombe, Rick P
2021-08-24 17:37             ` Mike Rapoport [this message]
2021-08-24 16:12   ` Vlastimil Babka
2021-08-25  8:43   ` David Hildenbrand
2021-08-23 13:25 ` [RFC PATCH 4/4] x86/mm: write protect (most) page tables Mike Rapoport
2021-08-23 20:08   ` Edgecombe, Rick P
2021-08-23 23:50   ` Dave Hansen
2021-08-24  3:34     ` Andy Lutomirski
2021-08-25 14:59       ` Dave Hansen
2021-08-24 13:32     ` Mike Rapoport
2021-08-25  8:38     ` David Hildenbrand
2021-08-26  8:02     ` Mike Rapoport
2021-08-26  9:01       ` Vlastimil Babka
     [not found]   ` <FB6C09CD-9CEA-4FE8-B179-98DB63EBDD68@gmail.com>
2021-08-24  5:34     ` Nadav Amit
2021-08-24 13:36       ` Mike Rapoport
2021-08-23 20:02 ` [RFC PATCH 0/4] mm/page_alloc: cache pte-mapped allocations Edgecombe, Rick P
2021-08-24 13:03   ` Mike Rapoport
2021-08-24 16:09 ` Vlastimil Babka
2021-08-29  7:06   ` Mike Rapoport

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