linux-kernel - Re: [PATCH 3/3] s390: supplement for ptdesc conversion

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Date: Wed, 27 Mar 2024 10:11:13 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Vishal Moola <vishal.moola@...il.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, david@...hat.com,
 rppt@...nel.org, willy@...radead.org, muchun.song@...ux.dev,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org,
 linux-s390@...r.kernel.org
Subject: Re: [PATCH 3/3] s390: supplement for ptdesc conversion



On 2024/3/27 03:48, Vishal Moola wrote:
> On Mon, Mar 04, 2024 at 07:07:20PM +0800, Qi Zheng wrote:
>> --- a/arch/s390/mm/gmap.c
>> +++ b/arch/s390/mm/gmap.c
>> @@ -206,9 +206,11 @@ static void gmap_free(struct gmap *gmap)
>>   
>>   	/* Free additional data for a shadow gmap */
>>   	if (gmap_is_shadow(gmap)) {
>> +		struct ptdesc *ptdesc;
>> +
>>   		/* Free all page tables. */
>> -		list_for_each_entry_safe(page, next, &gmap->pt_list, lru)
>> -			page_table_free_pgste(page);
>> +		list_for_each_entry_safe(ptdesc, next, &gmap->pt_list, pt_list)
>> +			page_table_free_pgste(ptdesc);
> 
> An important note: ptdesc allocation/freeing is different than the
> standard alloc_pages()/free_pages() routines architectures are used to.
> Are we sure we don't have memory leaks here?
> 
> We always allocate and free ptdescs as compound pages; for page table
> struct pages, most archictectures do not. s390 has CRST_ALLOC_ORDER
> pagetables, meaning if we free anything using the ptdesc api, we better
> be sure it was allocated using the ptdesc api as well.

According to the code inspection, all ptdescs added to the pmap->pt_list
are allocated via page_table_alloc_pgste().

> 
> Like you, I don't have a s390 to test on, so hopefully some s390 expert
> can chime in to let us know if we need a fix for this.

Yes, hope so!