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From:   Zi Yan <ziy@nvidia.com>
To:     Doug Berger <opendmb@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Rob Herring <robh+dt@kernel.org>,
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        Mike Rapoport <rppt@kernel.org>,
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        Florian Fainelli <f.fainelli@gmail.com>,
        David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Hari Bathini <hbathini@linux.ibm.com>,
        Kees Cook <keescook@chromium.org>,
        - <devicetree-spec@vger.kernel.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Mel Gorman <mgorman@suse.de>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        linux-mm@kvack.org, iommu@lists.linux.dev
Subject: Re: [PATCH 01/21] mm/page_isolation: protect cma from
 isolate_single_pageblock
Date:   Tue, 13 Sep 2022 21:53:55 -0400
Message-ID: <819CB6CD-0112-4B07-BDFE-84611470070F@nvidia.com>
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On 13 Sep 2022, at 21:47, Doug Berger wrote:

> On 9/13/2022 6:09 PM, Zi Yan wrote:
>> On 13 Sep 2022, at 20:59, Doug Berger wrote:
>>
>>> On 9/13/2022 5:02 PM, Zi Yan wrote:
>>>> On 13 Sep 2022, at 15:54, Doug Berger wrote:
>>>>
>>>>> The function set_migratetype_isolate() has special handling for
>>>>> pageblocks of MIGRATE_CMA type that protects them from being
>>>>> isolated for MIGRATE_MOVABLE requests.
>>>>>
>>>>> Since isolate_single_pageblock() doesn't receive the migratetype
>>>>> argument of start_isolate_page_range() it used the migratetype
>>>>> of the pageblock instead of the requested migratetype which
>>>>> defeats this MIGRATE_CMA check.
>>>>>
>>>>> This allows an attempt to create a gigantic page within a CMA
>>>>> region to change the migratetype of the first and last pageblocks
>>>>> from MIGRATE_CMA to MIGRATE_MOVABLE when they are restored after
>>>>> failure, which corrupts the CMA region.
>>>>>
>>>>> The calls to (un)set_migratetype_isolate() for the first and last
>>>>> pageblocks of the start_isolate_page_range() are moved back into
>>>>> that function to allow access to its migratetype argument and make
>>>>> it easier to see how all of the pageblocks in the range are
>>>>> isolated.
>>>>>
>>>>> Fixes: b2c9e2fbba32 ("mm: make alloc_contig_range work at pageblock=
 granularity")
>>>>> Signed-off-by: Doug Berger <opendmb@gmail.com>
>>>>> ---
>>>>>    mm/page_isolation.c | 75 +++++++++++++++++++++------------------=
------
>>>>>    1 file changed, 35 insertions(+), 40 deletions(-)
>>>>
>>>> Thanks for the fix.
>>> Thanks for the review.
>>>
>>>>
>>>> Why not just pass migratetype into isolate_single_pageblock() and us=
e
>>>> it when set_migratetype_isolate() is used? That would have much
>>>> fewer changes. What is the reason of pulling skip isolation logic ou=
t?
>>> I found the skip_isolation logic confusing and thought that setting a=
nd restoring the migratetype within the same function and consolidating t=
he error recovery paths also within that function was easier to understan=
d and less prone to accidental breakage.
>>>
>>> In particular, setting MIGRATE_ISOLATE in isolate_single_pageblock() =
and having to remember to unset it in start_isolate_page_range() differen=
tly on different error paths was troublesome for me.
>>
>> Wouldn't this work as well?
>>
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index c1307d1bea81..a312cabd0d95 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -288,6 +288,7 @@ __first_valid_page(unsigned long pfn, unsigned lon=
g nr_pages)
>>    * @isolate_before:    isolate the pageblock before the boundary_pfn=

>>    * @skip_isolation:    the flag to skip the pageblock isolation in s=
econd
>>    *                     isolate_single_pageblock()
>> + * @migratetype:       Migrate type to set in error recovery.
>>    *
>>    * Free and in-use pages can be as big as MAX_ORDER and contain more=
 than one
>>    * pageblock. When not all pageblocks within a page are isolated at =
the same
>> @@ -302,9 +303,9 @@ __first_valid_page(unsigned long pfn, unsigned lon=
g nr_pages)
>>    * the in-use page then splitting the free page.
>>    */
>>   static int isolate_single_pageblock(unsigned long boundary_pfn, int =
flags,
>> -                       gfp_t gfp_flags, bool isolate_before, bool ski=
p_isolation)
>> +                       gfp_t gfp_flags, bool isolate_before, bool ski=
p_isolation,
>> +                       int migratetype)
>>   {
>> -       unsigned char saved_mt;
>>          unsigned long start_pfn;
>>          unsigned long isolate_pageblock;
>>          unsigned long pfn;
>> @@ -328,12 +329,10 @@ static int isolate_single_pageblock(unsigned lon=
g boundary_pfn, int flags,
>>          start_pfn  =3D max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR=
_PAGES),
>>                                        zone->zone_start_pfn);
>>
>> -       saved_mt =3D get_pageblock_migratetype(pfn_to_page(isolate_pag=
eblock));
>> -
>>          if (skip_isolation)
>> -               VM_BUG_ON(!is_migrate_isolate(saved_mt));
>> +               VM_BUG_ON(!is_migrate_isolate(get_pageblock_migratetyp=
e(pfn_to_page(isolate_pageblock))));
>>          else {
>> -               ret =3D set_migratetype_isolate(pfn_to_page(isolate_pa=
geblock), saved_mt, flags,
>> +               ret =3D set_migratetype_isolate(pfn_to_page(isolate_pa=
geblock), migratetype, flags,
>>                                  isolate_pageblock, isolate_pageblock =
+ pageblock_nr_pages);
>>
>>                  if (ret)
>> @@ -475,7 +474,7 @@ static int isolate_single_pageblock(unsigned long =
boundary_pfn, int flags,
>>   failed:
>>          /* restore the original migratetype */
>>          if (!skip_isolation)
>> -               unset_migratetype_isolate(pfn_to_page(isolate_pagebloc=
k), saved_mt);
>> +               unset_migratetype_isolate(pfn_to_page(isolate_pagebloc=
k), migratetype);
>>          return -EBUSY;
>>   }
>>
>> @@ -537,7 +536,8 @@ int start_isolate_page_range(unsigned long start_p=
fn, unsigned long end_pfn,
>>          bool skip_isolation =3D false;
>>
>>          /* isolate [isolate_start, isolate_start + pageblock_nr_pages=
) pageblock */
>> -       ret =3D isolate_single_pageblock(isolate_start, flags, gfp_fla=
gs, false, skip_isolation);
>> +       ret =3D isolate_single_pageblock(isolate_start, flags, gfp_fla=
gs, false,
>> +                               skip_isolation, migratetype);
>>          if (ret)
>>                  return ret;
>>
>> @@ -545,7 +545,8 @@ int start_isolate_page_range(unsigned long start_p=
fn, unsigned long end_pfn,
>>                  skip_isolation =3D true;
>>
>>          /* isolate [isolate_end - pageblock_nr_pages, isolate_end) pa=
geblock */
>> -       ret =3D isolate_single_pageblock(isolate_end, flags, gfp_flags=
, true, skip_isolation);
>> +       ret =3D isolate_single_pageblock(isolate_end, flags, gfp_flags=
, true,
>> +                               skip_isolation, migratetype);
>>          if (ret) {
>>                  unset_migratetype_isolate(pfn_to_page(isolate_start),=
 migratetype);
>>                  return ret;
>>
> I would expect this to work as well, but it is not my preference.
>
>>>
>>> It could certainly be done differently, but this was my preference.
>>
>> A smaller patch can make review easier, right?
> It certainly can. Especially when it is for code that you are familiar =
with ;).
>
> I am happy to have you submit a patch to fix this issue and submit it t=
o stable for backporting. Fixing the issue is what's important to me.
>

I can submit the above as a patch. Is there a visible userspace issue, so=
 that we need to
backport it? Thanks.

>>
>>>>
>>>> Ultimately, I would like to make MIGRATE_ISOLATE a separate bit,
>>>> so that migratetype will not be overwritten during page isolation.
>>>> Then, set_migratetype_isolate() and start_isolate_page_range()
>>>> will not have migratetype to set in error recovery any more.
>>>> That is on my TODO.
>>>>
>>>>>
>>>>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>>>>> index 9d73dc38e3d7..8e16aa22cb61 100644
>>>>> --- a/mm/page_isolation.c
>>>>> +++ b/mm/page_isolation.c
>>>>> @@ -286,8 +286,6 @@ __first_valid_page(unsigned long pfn, unsigned =
long nr_pages)
>>>>>     * @flags:			isolation flags
>>>>>     * @gfp_flags:			GFP flags used for migrating pages
>>>>>     * @isolate_before:	isolate the pageblock before the boundary_pf=
n
>>>>> - * @skip_isolation:	the flag to skip the pageblock isolation in se=
cond
>>>>> - *			isolate_single_pageblock()
>>>>>     *
>>>>>     * Free and in-use pages can be as big as MAX_ORDER-1 and contai=
n more than one
>>>>>     * pageblock. When not all pageblocks within a page are isolated=
 at the same
>>>>> @@ -302,9 +300,8 @@ __first_valid_page(unsigned long pfn, unsigned =
long nr_pages)
>>>>>     * the in-use page then splitting the free page.
>>>>>     */
>>>>>    static int isolate_single_pageblock(unsigned long boundary_pfn, =
int flags,
>>>>> -			gfp_t gfp_flags, bool isolate_before, bool skip_isolation)
>>>>> +			gfp_t gfp_flags, bool isolate_before)
>>>>>    {
>>>>> -	unsigned char saved_mt;
>>>>>    	unsigned long start_pfn;
>>>>>    	unsigned long isolate_pageblock;
>>>>>    	unsigned long pfn;
>>>>> @@ -328,18 +325,6 @@ static int isolate_single_pageblock(unsigned l=
ong boundary_pfn, int flags,
>>>>>    	start_pfn  =3D max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR_P=
AGES),
>>>>>    				      zone->zone_start_pfn);
>>>>>
>>>>> -	saved_mt =3D get_pageblock_migratetype(pfn_to_page(isolate_pagebl=
ock));
>>>>> -
>>>>> -	if (skip_isolation)
>>>>> -		VM_BUG_ON(!is_migrate_isolate(saved_mt));
>>>>> -	else {
>>>>> -		ret =3D set_migratetype_isolate(pfn_to_page(isolate_pageblock), =
saved_mt, flags,
>>>>> -				isolate_pageblock, isolate_pageblock + pageblock_nr_pages);
>>>>> -
>>>>> -		if (ret)
>>>>> -			return ret;
>>>>> -	}
>>>>> -
>>>>>    	/*
>>>>>    	 * Bail out early when the to-be-isolated pageblock does not fo=
rm
>>>>>    	 * a free or in-use page across boundary_pfn:
>>>>> @@ -428,7 +413,7 @@ static int isolate_single_pageblock(unsigned lo=
ng boundary_pfn, int flags,
>>>>>    					ret =3D set_migratetype_isolate(page, page_mt,
>>>>>    						flags, head_pfn, head_pfn + nr_pages);
>>>>>    					if (ret)
>>>>> -						goto failed;
>>>>> +						return ret;
>>>>>    				}
>>>>>
>>>>>    				ret =3D __alloc_contig_migrate_range(&cc, head_pfn,
>>>>> @@ -443,7 +428,7 @@ static int isolate_single_pageblock(unsigned lo=
ng boundary_pfn, int flags,
>>>>>    					unset_migratetype_isolate(page, page_mt);
>>>>>
>>>>>    				if (ret)
>>>>> -					goto failed;
>>>>> +					return -EBUSY;
>>>>>    				/*
>>>>>    				 * reset pfn to the head of the free page, so
>>>>>    				 * that the free page handling code above can split
>>>>> @@ -459,24 +444,19 @@ static int isolate_single_pageblock(unsigned =
long boundary_pfn, int flags,
>>>>>    				while (!PageBuddy(pfn_to_page(outer_pfn))) {
>>>>>    					/* stop if we cannot find the free page */
>>>>>    					if (++order >=3D MAX_ORDER)
>>>>> -						goto failed;
>>>>> +						return -EBUSY;
>>>>>    					outer_pfn &=3D ~0UL << order;
>>>>>    				}
>>>>>    				pfn =3D outer_pfn;
>>>>>    				continue;
>>>>>    			} else
>>>>>    #endif
>>>>> -				goto failed;
>>>>> +				return -EBUSY;
>>>>>    		}
>>>>>
>>>>>    		pfn++;
>>>>>    	}
>>>>>    	return 0;
>>>>> -failed:
>>>>> -	/* restore the original migratetype */
>>>>> -	if (!skip_isolation)
>>>>> -		unset_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_=
mt);
>>>>> -	return -EBUSY;
>>>>>    }
>>>>>
>>>>>    /**
>>>>> @@ -534,21 +514,30 @@ int start_isolate_page_range(unsigned long st=
art_pfn, unsigned long end_pfn,
>>>>>    	unsigned long isolate_start =3D ALIGN_DOWN(start_pfn, pageblock=
_nr_pages);
>>>>>    	unsigned long isolate_end =3D ALIGN(end_pfn, pageblock_nr_pages=
);
>>>>>    	int ret;
>>>>> -	bool skip_isolation =3D false;
>>>>>
>>>>>    	/* isolate [isolate_start, isolate_start + pageblock_nr_pages) =
pageblock */
>>>>> -	ret =3D isolate_single_pageblock(isolate_start, flags, gfp_flags,=
 false, skip_isolation);
>>>>> +	ret =3D set_migratetype_isolate(pfn_to_page(isolate_start), migra=
tetype,
>>>>> +			flags, isolate_start, isolate_start + pageblock_nr_pages);
>>>>>    	if (ret)
>>>>>    		return ret;
>>>>> -
>>>>> -	if (isolate_start =3D=3D isolate_end - pageblock_nr_pages)
>>>>> -		skip_isolation =3D true;
>>>>> +	ret =3D isolate_single_pageblock(isolate_start, flags, gfp_flags,=
 false);
>>>>> +	if (ret)
>>>>> +		goto unset_start_block;
>>>>>
>>>>>    	/* isolate [isolate_end - pageblock_nr_pages, isolate_end) page=
block */
>>>>> -	ret =3D isolate_single_pageblock(isolate_end, flags, gfp_flags, t=
rue, skip_isolation);
>>>>> +	pfn =3D isolate_end - pageblock_nr_pages;
>>>>> +	if (isolate_start !=3D pfn) {
>>>>> +		ret =3D set_migratetype_isolate(pfn_to_page(pfn), migratetype,
>>>>> +				flags, pfn, pfn + pageblock_nr_pages);
>>>>> +		if (ret)
>>>>> +			goto unset_start_block;
>>>>> +	}
>>>>> +	ret =3D isolate_single_pageblock(isolate_end, flags, gfp_flags, t=
rue);
>>>>>    	if (ret) {
>>>>> -		unset_migratetype_isolate(pfn_to_page(isolate_start), migratetyp=
e);
>>>>> -		return ret;
>>>>> +		if (isolate_start !=3D pfn)
>>>>> +			goto unset_end_block;
>>>>> +		else
>>>>> +			goto unset_start_block;
>>>>>    	}
>>>>>
>>>>>    	/* skip isolated pageblocks at the beginning and end */
>>>>> @@ -557,15 +546,21 @@ int start_isolate_page_range(unsigned long st=
art_pfn, unsigned long end_pfn,
>>>>>    	     pfn +=3D pageblock_nr_pages) {
>>>>>    		page =3D __first_valid_page(pfn, pageblock_nr_pages);
>>>>>    		if (page && set_migratetype_isolate(page, migratetype, flags,
>>>>> -					start_pfn, end_pfn)) {
>>>>> -			undo_isolate_page_range(isolate_start, pfn, migratetype);
>>>>> -			unset_migratetype_isolate(
>>>>> -				pfn_to_page(isolate_end - pageblock_nr_pages),
>>>>> -				migratetype);
>>>>> -			return -EBUSY;
>>>>> -		}
>>>>> +					start_pfn, end_pfn))
>>>>> +			goto unset_isolated_blocks;
>>>>>    	}
>>>>>    	return 0;
>>>>> +
>>>>> +unset_isolated_blocks:
>>>>> +	ret =3D -EBUSY;
>>>>> +	undo_isolate_page_range(isolate_start + pageblock_nr_pages, pfn,
>>>>> +				migratetype);
>>>>> +unset_end_block:
>>>>> +	unset_migratetype_isolate(pfn_to_page(isolate_end - pageblock_nr_=
pages),
>>>>> +				  migratetype);
>>>>> +unset_start_block:
>>>>> +	unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype=
);
>>>>> +	return ret;
>>>>>    }
>>>>>
>>>>>    /*
>>>>> -- =

>>>>> 2.25.1
>>>>
>>>>
>>>> --
>>>> Best Regards,
>>>> Yan, Zi
>>
>>
>> --
>> Best Regards,
>> Yan, Zi
> Thanks for your efforts to get alloc_contig_range to work at pageblock =
granularity!
> -Doug


--
Best Regards,
Yan, Zi

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