linux-kernel - Re: [syzbot] [mm?] BUG: Bad page map (7)

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Message-ID: <5f8423f1-26d1-2116-ce63-bfb4d5bc2634@intel.com>
Date:   Mon, 11 Sep 2023 15:32:22 +0800
From:   Yin Fengwei <fengwei.yin@...el.com>
To:     Matthew Wilcox <willy@...radead.org>,
        syzbot <syzbot+55cc72f8cc3a549119df@...kaller.appspotmail.com>
CC:     <akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] [mm?] BUG: Bad page map (7)



On 9/11/23 15:24, Yin Fengwei wrote:
> Hi Matthew,
> 
> On 9/10/23 11:02, Matthew Wilcox wrote:
>> On Sat, Sep 09, 2023 at 10:12:48AM -0700, syzbot wrote:
>>> commit 617c28ecab22d98a3809370eb6cb50fa24b7bfe1
>>> Author: Yin Fengwei <fengwei.yin@...el.com>
>>> Date:   Wed Aug 2 15:14:05 2023 +0000
>>>
>>>     filemap: batch PTE mappings
>>
>> Hmm ... I don't know if this is the bug, but ...
> I do think we should merge your patch here. LKP already noticed some performance
> regressions. I suppose this patch can fix some of them.
I will verify this patch to see whether the regressions noticed by LKP can be
fixed. Will keep you updated for any progress. Thanks.


Regards
Yin, Fengwei

> 
> 
> I root caused the this "bad page map" issue in my local env. It's related with pte
> with protnone on x86_64. So if pte is not protnone, advancing pte by adding
> 1UL << PFN_PTE_SHIFT is correct. But if pte is protnone, should subtract
> 1UL << PFN_PTE_SHIFT. I saw pfn_pte() had pfn ^= protnone_mask() and just realized
> it.
> 
> 
> The producer mmap with PROT_NONE and then trigger SIGXFSZ and create core file.
> That will cause GUP with FOLL_FORCE and create protnone pte.
> 
> I submitted request to sysbot to test the fixing worked on my local env. Thanks.
> 
> 
> Regards
> Yin, Fengwei
> 
>>
>> #syz test
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index 582f5317ff71..580d0b2b1a7c 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -3506,7 +3506,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>>  		if (count) {
>>  			set_pte_range(vmf, folio, page, count, addr);
>>  			folio_ref_add(folio, count);
>> -			if (in_range(vmf->address, addr, count))
>> +			if (in_range(vmf->address, addr, count * PAGE_SIZE))
>>  				ret = VM_FAULT_NOPAGE;
>>  		}
>>  
>> @@ -3520,7 +3520,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>>  	if (count) {
>>  		set_pte_range(vmf, folio, page, count, addr);
>>  		folio_ref_add(folio, count);
>> -		if (in_range(vmf->address, addr, count))
>> +		if (in_range(vmf->address, addr, count * PAGE_SIZE))
>>  			ret = VM_FAULT_NOPAGE;
>>  	}
>>  
>>