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From: Michal Hocko <mhocko@kernel.org>
To: Bob Liu <lliubbo@gmail.com>, Will Deacon <will.deacon@arm.com>
Cc: Wang Nan <wangnan0@huawei.com>, Linux-MM <linux-mm@kvack.org>,
	Linux-Kernel <linux-kernel@vger.kernel.org>,
	Bob Liu <liubo95@huawei.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Ingo Molnar <mingo@kernel.org>, Roman Gushchin <guro@fb.com>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [RFC PATCH] mm, oom_reaper: gather each vma to prevent leaking TLB entry
Date: Mon, 6 Nov 2017 13:27:26 +0100	[thread overview]
Message-ID: <20171106122726.jwe2ecymlu7qclkk@dhcp22.suse.cz> (raw)
In-Reply-To: <20171106085251.jwrpgne4dnl4gopy@dhcp22.suse.cz>

On Mon 06-11-17 09:52:51, Michal Hocko wrote:
> On Mon 06-11-17 15:04:40, Bob Liu wrote:
> > On Mon, Nov 6, 2017 at 11:36 AM, Wang Nan <wangnan0@huawei.com> wrote:
> > > tlb_gather_mmu(&tlb, mm, 0, -1) means gathering all virtual memory space.
> > > In this case, tlb->fullmm is true. Some archs like arm64 doesn't flush
> > > TLB when tlb->fullmm is true:
> > >
> > >   commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1").
> > >
> > 
> > CC'ed Will Deacon.
> > 
> > > Which makes leaking of tlb entries. For example, when oom_reaper
> > > selects a task and reaps its virtual memory space, another thread
> > > in this task group may still running on another core and access
> > > these already freed memory through tlb entries.
> 
> No threads should be running in userspace by the time the reaper gets to
> unmap their address space. So the only potential case is they are
> accessing the user memory from the kernel when we should fault and we
> have MMF_UNSTABLE to cause a SIGBUS.

I hope we have clarified that the tasks are not running in userspace at
the time of reaping. I am still wondering whether this is real from the
kernel space via copy_{from,to}_user. Is it possible we won't fault?
I am not sure I understand what "Given that the ASID allocator will
never re-allocate a dirty ASID" means exactly. Will, could you clarify
please?
-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org>
To: Bob Liu <lliubbo@gmail.com>, Will Deacon <will.deacon@arm.com>
Cc: Wang Nan <wangnan0@huawei.com>, Linux-MM <linux-mm@kvack.org>,
	Linux-Kernel <linux-kernel@vger.kernel.org>,
	Bob Liu <liubo95@huawei.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Ingo Molnar <mingo@kernel.org>, Roman Gushchin <guro@fb.com>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [RFC PATCH] mm, oom_reaper: gather each vma to prevent leaking TLB entry
Date: Mon, 6 Nov 2017 13:27:26 +0100	[thread overview]
Message-ID: <20171106122726.jwe2ecymlu7qclkk@dhcp22.suse.cz> (raw)
In-Reply-To: <20171106085251.jwrpgne4dnl4gopy@dhcp22.suse.cz>

On Mon 06-11-17 09:52:51, Michal Hocko wrote:
> On Mon 06-11-17 15:04:40, Bob Liu wrote:
> > On Mon, Nov 6, 2017 at 11:36 AM, Wang Nan <wangnan0@huawei.com> wrote:
> > > tlb_gather_mmu(&tlb, mm, 0, -1) means gathering all virtual memory space.
> > > In this case, tlb->fullmm is true. Some archs like arm64 doesn't flush
> > > TLB when tlb->fullmm is true:
> > >
> > >   commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1").
> > >
> > 
> > CC'ed Will Deacon.
> > 
> > > Which makes leaking of tlb entries. For example, when oom_reaper
> > > selects a task and reaps its virtual memory space, another thread
> > > in this task group may still running on another core and access
> > > these already freed memory through tlb entries.
> 
> No threads should be running in userspace by the time the reaper gets to
> unmap their address space. So the only potential case is they are
> accessing the user memory from the kernel when we should fault and we
> have MMF_UNSTABLE to cause a SIGBUS.

I hope we have clarified that the tasks are not running in userspace at
the time of reaping. I am still wondering whether this is real from the
kernel space via copy_{from,to}_user. Is it possible we won't fault?
I am not sure I understand what "Given that the ASID allocator will
never re-allocate a dirty ASID" means exactly. Will, could you clarify
please?
-- 
Michal Hocko
SUSE Labs

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  parent reply	other threads:[~2017-11-06 12:27 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-06  3:36 [RFC PATCH] mm, oom_reaper: gather each vma to prevent leaking TLB entry Wang Nan
2017-11-06  3:36 ` Wang Nan
2017-11-06  7:04 ` Bob Liu
2017-11-06  7:04   ` Bob Liu
2017-11-06  8:52   ` Michal Hocko
2017-11-06  8:52     ` Michal Hocko
2017-11-06  9:59     ` Wangnan (F)
2017-11-06  9:59       ` Wangnan (F)
2017-11-06 10:40       ` Michal Hocko
2017-11-06 10:40         ` Michal Hocko
2017-11-06 11:03         ` Wangnan (F)
2017-11-06 11:03           ` Wangnan (F)
2017-11-06 11:57           ` Michal Hocko
2017-11-06 11:57             ` Michal Hocko
2017-11-07  3:51             ` Wangnan (F)
2017-11-07  3:51               ` Wangnan (F)
2017-11-06 12:27     ` Michal Hocko [this message]
2017-11-06 12:27       ` Michal Hocko
2017-11-07  0:54       ` Will Deacon
2017-11-07  0:54         ` Will Deacon
2017-11-07  7:54         ` Michal Hocko
2017-11-07  7:54           ` Michal Hocko

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