linux-kernel - Re: [PATCH 2/2] mm: convert do_set

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <569e592c-1c30-4c03-bcee-c1670ac4e159@linux.alibaba.com>
Date: Thu, 8 May 2025 10:23:28 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: akpm@...ux-foundation.org, david@...hat.com, hannes@...xchg.org,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, npache@...hat.com,
 ryan.roberts@....com, dev.jain@....com, ziy@...dia.com, vbabka@...e.cz,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: convert do_set_pmd() to take a folio



On 2025/5/8 00:47, Matthew Wilcox wrote:
> On Wed, May 07, 2025 at 08:36:54PM +0800, Baolin Wang wrote:
>> On 2025/5/7 20:10, Matthew Wilcox wrote:
>>> Because I see nowhere in this patch that you initialise 'page'.
>>
>> Please look at the following code in do_set_pmd(), and the 'page' will be
>> initialized before using.
>>
>>          if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags))
>>                  return ret;
>>
>>          if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
>>                  return ret;
>>
>>          if (folio_order(folio) != HPAGE_PMD_ORDER)
>>                  return ret;
>>          page = &folio->page;
> 
> Ah, fair, I missed that.
> 
>>> And that's really the important part.  You seem to be assuming that a
>>> folio will never be larger than PMD size, and I'm not comfortable with
>>
>> No, I have no this assumption. But do_set_pmd() is used to establish PMD
>> mappings for the PMD-sized folios, and we already have PMD-sized checks to
>> validate the folio size:
>>
>>          if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
>>                  return ret;
>>
>>          if (folio_order(folio) != HPAGE_PMD_ORDER)
>>                  return ret;
>>
>>> that assumption.  It's a limitation I put in place a few years ago so we
>>> didn't have to find and fix all those assumptions immediately, but I
>>> imagine that some day we'll want to have larger folios.
>>>
>>> So unless you can derive _which_ page in the folio we want to map from
>>
>> IMO, for PMD mapping of a PMD-sized folio, we do not need to know _which_
>> page in the folio we want to map, because we'll always map the entire
>> PMD-sized folio.
> 
> There's a difference between "Assert that the folio is PMD sized" inside
> the function because we know there are still problems, and "Change the
> interface so we can't specify which page inside the folio is the one
> we're actually interested in".

Fair enough. So how about adding a new 'folio' parameter to 
do_set_pmd(), similar to the set_pte_range() function prototype?

vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct 
page *page)

> I reiterate the NACK to this patch.