linux-kernel - Re: [External] Re: [PATCH v19 7/8] mm: hugetlb: add a kernel parameter hugetlb_free

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 for Android: free password hash cracker in your pocket

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

Message-ID: <e9af16bb-2296-c9fb-976f-f99472490940@redhat.com>
Date:   Fri, 19 Mar 2021 13:36:18 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Muchun Song <songmuchun@...edance.com>,
        Oscar Salvador <osalvador@...e.de>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, bp@...en8.de,
        X86 ML <x86@...nel.org>, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Chen Huang <chenhuang5@...wei.com>,
        Bodeddula Balasubramaniam <bodeddub@...zon.com>
Subject: Re: [External] Re: [PATCH v19 7/8] mm: hugetlb: add a kernel
 parameter hugetlb_free_vmemmap

On 19.03.21 13:15, Muchun Song wrote:
> On Fri, Mar 19, 2021 at 4:59 PM Oscar Salvador <osalvador@...e.de> wrote:
>>
>> On Mon, Mar 15, 2021 at 05:20:14PM +0800, Muchun Song wrote:
>>> --- a/arch/x86/mm/init_64.c
>>> +++ b/arch/x86/mm/init_64.c
>>> @@ -34,6 +34,7 @@
>>>   #include <linux/gfp.h>
>>>   #include <linux/kcore.h>
>>>   #include <linux/bootmem_info.h>
>>> +#include <linux/hugetlb.h>
>>>
>>>   #include <asm/processor.h>
>>>   #include <asm/bios_ebda.h>
>>> @@ -1557,7 +1558,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>>>   {
>>>        int err;
>>>
>>> -     if (end - start < PAGES_PER_SECTION * sizeof(struct page))
>>> +     if ((is_hugetlb_free_vmemmap_enabled()  && !altmap) ||
>>> +         end - start < PAGES_PER_SECTION * sizeof(struct page))
>>>                err = vmemmap_populate_basepages(start, end, node, NULL);
>>>        else if (boot_cpu_has(X86_FEATURE_PSE))
>>>                err = vmemmap_populate_hugepages(start, end, node, altmap);
>>
>> I've been thinking about this some more.
>>
>> Assume you opt-in the hugetlb-vmemmap feature, and assume you pass a valid altmap
>> to vmemmap_populate.
>> This will lead to use populating the vmemmap array with hugepages.
> 
> Right.
> 
>>
>> What if then, a HugeTLB gets allocated and falls within that memory range (backed
>> by hugetpages)?
> 
> I am not sure whether we can allocate the HugeTLB pages from there.
> Will only device memory pass a valid altmap parameter to
> vmemmap_populate()? If yes, can we allocate HugeTLB pages from
> device memory? Sorry, I am not an expert on this.

I think, right now, yes. System RAM that's applicable for HugePages 
never uses an altmap. But Oscar's patch will change that, maybe before 
your series might get included from what I've been reading. [1]

[1] https://lkml.kernel.org/r/20210319092635.6214-1-osalvador@suse.de

> 
> 
>> AFAIK, this will get us in trouble as currently the code can only operate on memory
>> backed by PAGE_SIZE pages, right?
>>
>> I cannot remember, but I do not think nothing prevents that from happening?
>> Am I missing anything?
> 
> Maybe David H is more familiar with this.
> 
> Hi David,
> 
> Do you have some suggestions on this?

There has to be some way to identify whether we can optimize specific 
vmemmap pages or should just leave them alone. altmap vs. !altmap.

Unfortunately, there is no easy way to detect that - e.g., 
PageReserved() applies also to boot memory.

We could go back to setting a special PageType for these vmemmap pages, 
indicating "this is a page allocated from an altmap, don't touch it".

-- 
Thanks,

David / dhildenb