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From: Catalin Marinas <catalin.marinas@arm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Jianyong Wu <Jianyong.Wu@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>, Justin He <Justin.He@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	Anshuman Khandual <Anshuman.Khandual@arm.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"quic_qiancai@quicinc.com" <quic_qiancai@quicinc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	 "gshan@redhat.com" <gshan@redhat.com>, nd <nd@arm.com>
Subject: Re: [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping
Date: Thu, 27 Jan 2022 12:34:28 +0000	[thread overview]
Message-ID: <YfKRVJlWrgluqD9e@arm.com> (raw)
In-Reply-To: <ca62449b-7ab0-0e18-ee5a-b46b3f527385@redhat.com>

On Thu, Jan 27, 2022 at 01:22:47PM +0100, David Hildenbrand wrote:
> > Yes, system_state can roughly separate these callers of __create_pgd_mapping. When system_state > SYSTEM_BOOTING we can add the lock.
> > Thus, I have the following change:
> > 
> > static DEFINE_SPINLOCK(swapper_pgdir_lock);
> > +static DEFINE_MUTEX(fixmap_lock);
> > 
> >  void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
> >  {
> > @@ -329,6 +330,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
> >         }
> >         BUG_ON(p4d_bad(p4d));
> > 
> > +       if (system_state > SYSTEM_BOOTING)
> 
> As there is nothing smaller than SYSTEM_BOOTING, you can use
> 	if (system_state != SYSTEM_BOOTING)
> 
> ...
> 
> > 
> > It seems work and somehow simper. But I don't know if it is reasonable to do this. So, any idea? @Ard Biesheuvel  @Catalin Marinas 
> 
> It's worth looking at kernel/notifier.c, e.g.,
> blocking_notifier_chain_register()
> 
> if (unlikely(system_state == SYSTEM_BOOTING))
> 	return notifier_chain_register(&nh->head, n);
> 
> down_write(&nh->rwsem);
> ret = notifier_chain_register(&nh->head, n);
> up_write(&nh->rwsem);
> 
> If we decide to go down that path, we should make sure to add a comment like
> 
> /*
>  * No need for locking during early boot. And it doesn't work as
>  * expected with KASLR enabled where we might clear BSS twice.
>  */

A similar approach sounds fine to me.

-- 
Catalin

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WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Jianyong Wu <Jianyong.Wu@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>, Justin He <Justin.He@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	Anshuman Khandual <Anshuman.Khandual@arm.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"quic_qiancai@quicinc.com" <quic_qiancai@quicinc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"gshan@redhat.com" <gshan@redhat.com>, nd <nd@arm.com>
Subject: Re: [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping
Date: Thu, 27 Jan 2022 12:34:28 +0000	[thread overview]
Message-ID: <YfKRVJlWrgluqD9e@arm.com> (raw)
In-Reply-To: <ca62449b-7ab0-0e18-ee5a-b46b3f527385@redhat.com>

On Thu, Jan 27, 2022 at 01:22:47PM +0100, David Hildenbrand wrote:
> > Yes, system_state can roughly separate these callers of __create_pgd_mapping. When system_state > SYSTEM_BOOTING we can add the lock.
> > Thus, I have the following change:
> > 
> > static DEFINE_SPINLOCK(swapper_pgdir_lock);
> > +static DEFINE_MUTEX(fixmap_lock);
> > 
> >  void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
> >  {
> > @@ -329,6 +330,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
> >         }
> >         BUG_ON(p4d_bad(p4d));
> > 
> > +       if (system_state > SYSTEM_BOOTING)
> 
> As there is nothing smaller than SYSTEM_BOOTING, you can use
> 	if (system_state != SYSTEM_BOOTING)
> 
> ...
> 
> > 
> > It seems work and somehow simper. But I don't know if it is reasonable to do this. So, any idea? @Ard Biesheuvel  @Catalin Marinas 
> 
> It's worth looking at kernel/notifier.c, e.g.,
> blocking_notifier_chain_register()
> 
> if (unlikely(system_state == SYSTEM_BOOTING))
> 	return notifier_chain_register(&nh->head, n);
> 
> down_write(&nh->rwsem);
> ret = notifier_chain_register(&nh->head, n);
> up_write(&nh->rwsem);
> 
> If we decide to go down that path, we should make sure to add a comment like
> 
> /*
>  * No need for locking during early boot. And it doesn't work as
>  * expected with KASLR enabled where we might clear BSS twice.
>  */

A similar approach sounds fine to me.

-- 
Catalin

  reply	other threads:[~2022-01-27 12:35 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-16  8:28 [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping Jianyong Wu
2021-12-16  8:28 ` Jianyong Wu
2021-12-16 15:19 ` David Hildenbrand
2021-12-16 15:19   ` David Hildenbrand
2021-12-17  9:30 ` Mark Rutland
2021-12-17  9:30   ` Mark Rutland
2021-12-17 10:09   ` Jianyong Wu
2021-12-17 10:09     ` Jianyong Wu
2022-01-05 18:03 ` Catalin Marinas
2022-01-05 18:03   ` Catalin Marinas
2022-01-06 10:13   ` Jianyong Wu
2022-01-06 10:13     ` Jianyong Wu
2022-01-06 15:56     ` Catalin Marinas
2022-01-06 15:56       ` Catalin Marinas
2022-01-07  9:10       ` Jianyong Wu
2022-01-07  9:10         ` Jianyong Wu
2022-01-07 10:42         ` Catalin Marinas
2022-01-07 10:42           ` Catalin Marinas
2022-01-26  4:20           ` Justin He
2022-01-26  4:20             ` Justin He
2022-01-26  8:36             ` Ard Biesheuvel
2022-01-26  8:36               ` Ard Biesheuvel
2022-01-26 10:09               ` Jianyong Wu
2022-01-26 10:09                 ` Jianyong Wu
2022-01-26 10:12                 ` Ard Biesheuvel
2022-01-26 10:12                   ` Ard Biesheuvel
2022-01-26 10:17                   ` David Hildenbrand
2022-01-26 10:17                     ` David Hildenbrand
2022-01-26 10:28                     ` Jianyong Wu
2022-01-26 10:28                       ` Jianyong Wu
2022-01-26 10:30                       ` David Hildenbrand
2022-01-26 10:30                         ` David Hildenbrand
2022-01-26 10:31                         ` David Hildenbrand
2022-01-26 10:31                           ` David Hildenbrand
2022-01-27  6:24                           ` Jianyong Wu
2022-01-27  6:24                             ` Jianyong Wu
2022-01-27 12:22                             ` David Hildenbrand
2022-01-27 12:22                               ` David Hildenbrand
2022-01-27 12:34                               ` Catalin Marinas [this message]
2022-01-27 12:34                                 ` Catalin Marinas
2022-01-31  8:13                                 ` Jianyong Wu
2022-01-31  8:13                                   ` Jianyong Wu
2022-01-31  8:10                               ` Jianyong Wu
2022-01-31  8:10                                 ` Jianyong Wu
2022-01-27  1:31               ` Justin He
2022-01-27  1:31                 ` Justin He
2022-01-07 10:53         ` Catalin Marinas
2022-01-07 10:53           ` Catalin Marinas

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