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Subject: Re: [RFC v3 PATCH 5/5] x86: check VM_DEAD flag in page fault
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Yang Shi <yang.shi@linux.alibaba.com>, willy@infradead.org,
        akpm@linux-foundation.org, peterz@infradead.org, mingo@redhat.com,
        acme@kernel.org, alexander.shishkin@linux.intel.com,
        jolsa@redhat.com, namhyung@kernel.org, tglx@linutronix.de,
        hpa@zytor.com, linux-mm@kvack.org, x86@kernel.org,
        linux-kernel@vger.kernel.org
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 <20180702121528.GM19043@dhcp22.suse.cz>
From:   Laurent Dufour <ldufour@linux.vnet.ibm.com>
Date:   Mon, 2 Jul 2018 14:26:09 +0200
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On 02/07/2018 14:15, Michal Hocko wrote:
> On Mon 02-07-18 10:45:03, Laurent Dufour wrote:
>> On 30/06/2018 00:39, Yang Shi wrote:
>>> Check VM_DEAD flag of vma in page fault handler, if it is set, trigger
>>> SIGSEGV.
>>>
>>> Cc: Michal Hocko <mhocko@kernel.org>
>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>> Cc: Ingo Molnar <mingo@redhat.com>
>>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>>> ---
>>>  arch/x86/mm/fault.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
>>> index 9a84a0d..3fd2da5 100644
>>> --- a/arch/x86/mm/fault.c
>>> +++ b/arch/x86/mm/fault.c
>>> @@ -1357,6 +1357,10 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs)
>>>  		bad_area(regs, error_code, address);
>>>  		return;
>>>  	}
>>> +	if (unlikely(vma->vm_flags & VM_DEAD)) {
>>> +		bad_area(regs, error_code, address);
>>> +		return;
>>> +	}
>>
>> This will have to be done for all the supported architectures, what about doing
>> this check in handle_mm_fault() and return VM_FAULT_SIGSEGV ?
> 
> We already do have a model for that. Have a look at MMF_UNSTABLE.

MMF_UNSTABLE is a mm's flag, here this is a VMA's flag which is checked.