| 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
| ||
|
Message-ID: <CAEvNRgHMdnALNfT0SuEb-gqM1Aq1c6U_nRB2GzC0jYqrDRJTOw@mail.gmail.com>
Date: Wed, 21 Jan 2026 16:20:19 -0800
From: Ackerley Tng <ackerleytng@...gle.com>
To: kalyazin@...zon.com, "Kalyazin, Nikita" <kalyazin@...zon.co.uk>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>, "kernel@...0n.name" <kernel@...0n.name>,
"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
"loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>
Cc: "pbonzini@...hat.com" <pbonzini@...hat.com>, "corbet@....net" <corbet@....net>,
"maz@...nel.org" <maz@...nel.org>, "oupton@...nel.org" <oupton@...nel.org>,
"joey.gouly@....com" <joey.gouly@....com>, "suzuki.poulose@....com" <suzuki.poulose@....com>,
"yuzenghui@...wei.com" <yuzenghui@...wei.com>, "catalin.marinas@....com" <catalin.marinas@....com>,
"will@...nel.org" <will@...nel.org>, "seanjc@...gle.com" <seanjc@...gle.com>,
"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>,
"hpa@...or.com" <hpa@...or.com>, "luto@...nel.org" <luto@...nel.org>,
"peterz@...radead.org" <peterz@...radead.org>, "willy@...radead.org" <willy@...radead.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "david@...nel.org" <david@...nel.org>,
"lorenzo.stoakes@...cle.com" <lorenzo.stoakes@...cle.com>,
"Liam.Howlett@...cle.com" <Liam.Howlett@...cle.com>, "vbabka@...e.cz" <vbabka@...e.cz>,
"rppt@...nel.org" <rppt@...nel.org>, "surenb@...gle.com" <surenb@...gle.com>, "mhocko@...e.com" <mhocko@...e.com>,
"ast@...nel.org" <ast@...nel.org>, "daniel@...earbox.net" <daniel@...earbox.net>,
"andrii@...nel.org" <andrii@...nel.org>, "martin.lau@...ux.dev" <martin.lau@...ux.dev>,
"eddyz87@...il.com" <eddyz87@...il.com>, "song@...nel.org" <song@...nel.org>,
"yonghong.song@...ux.dev" <yonghong.song@...ux.dev>,
"john.fastabend@...il.com" <john.fastabend@...il.com>, "kpsingh@...nel.org" <kpsingh@...nel.org>,
"sdf@...ichev.me" <sdf@...ichev.me>, "haoluo@...gle.com" <haoluo@...gle.com>,
"jolsa@...nel.org" <jolsa@...nel.org>, "jgg@...pe.ca" <jgg@...pe.ca>,
"jhubbard@...dia.com" <jhubbard@...dia.com>, "peterx@...hat.com" <peterx@...hat.com>,
"jannh@...gle.com" <jannh@...gle.com>, "pfalcato@...e.de" <pfalcato@...e.de>,
"shuah@...nel.org" <shuah@...nel.org>, "riel@...riel.com" <riel@...riel.com>,
"ryan.roberts@....com" <ryan.roberts@....com>, "jgross@...e.com" <jgross@...e.com>,
"yu-cheng.yu@...el.com" <yu-cheng.yu@...el.com>, "kas@...nel.org" <kas@...nel.org>,
"coxu@...hat.com" <coxu@...hat.com>, "kevin.brodsky@....com" <kevin.brodsky@....com>,
"maobibo@...ngson.cn" <maobibo@...ngson.cn>, "prsampat@....com" <prsampat@....com>,
"mlevitsk@...hat.com" <mlevitsk@...hat.com>, "jmattson@...gle.com" <jmattson@...gle.com>,
"jthoughton@...gle.com" <jthoughton@...gle.com>, "agordeev@...ux.ibm.com" <agordeev@...ux.ibm.com>,
"alex@...ti.fr" <alex@...ti.fr>, "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
"borntraeger@...ux.ibm.com" <borntraeger@...ux.ibm.com>, "chenhuacai@...nel.org" <chenhuacai@...nel.org>,
"dev.jain@....com" <dev.jain@....com>, "gor@...ux.ibm.com" <gor@...ux.ibm.com>,
"hca@...ux.ibm.com" <hca@...ux.ibm.com>,
"Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>, "palmer@...belt.com" <palmer@...belt.com>,
"pjw@...nel.org" <pjw@...nel.org>,
"shijie@...amperecomputing.com" <shijie@...amperecomputing.com>, "svens@...ux.ibm.com" <svens@...ux.ibm.com>,
"thuth@...hat.com" <thuth@...hat.com>, "wyihan@...gle.com" <wyihan@...gle.com>,
"yang@...amperecomputing.com" <yang@...amperecomputing.com>,
"vannapurve@...gle.com" <vannapurve@...gle.com>, "jackmanb@...gle.com" <jackmanb@...gle.com>,
"aneesh.kumar@...nel.org" <aneesh.kumar@...nel.org>, "patrick.roy@...ux.dev" <patrick.roy@...ux.dev>,
"Thomson, Jack" <jackabt@...zon.co.uk>, "Itazuri, Takahiro" <itazur@...zon.co.uk>,
"Manwaring, Derek" <derekmn@...zon.com>, "Cali, Marco" <xmarcalx@...zon.co.uk>
Subject: Re: [PATCH v9 02/13] mm/gup: drop secretmem optimization from gup_fast_folio_allowed
Nikita Kalyazin <kalyazin@...zon.com> writes:
> On 15/01/2026 21:40, Ackerley Tng wrote:
>> "Kalyazin, Nikita" <kalyazin@...zon.co.uk> writes:
>>
>>> From: Patrick Roy <patrick.roy@...ux.dev>
>>>
>>> This drops an optimization in gup_fast_folio_allowed() where
>>> secretmem_mapping() was only called if CONFIG_SECRETMEM=y. secretmem is
>>> enabled by default since commit b758fe6df50d ("mm/secretmem: make it on
>>> by default"), so the secretmem check did not actually end up elided in
>>> most cases anymore anyway.
>>>
>>> This is in preparation of the generalization of handling mappings where
>>> direct map entries of folios are set to not present. Currently,
>>> mappings that match this description are secretmem mappings
>>> (memfd_secret()). Later, some guest_memfd configurations will also fall
>>> into this category.
>>>
>>> Signed-off-by: Patrick Roy <patrick.roy@...ux.dev>
>>> Acked-by: Vlastimil Babka <vbabka@...e.cz>
>>> Signed-off-by: Nikita Kalyazin <kalyazin@...zon.com>
>>> ---
>>> mm/gup.c | 11 +----------
>>> 1 file changed, 1 insertion(+), 10 deletions(-)
>>>
>>> diff --git a/mm/gup.c b/mm/gup.c
>>> index 95d948c8e86c..9cad53acbc99 100644
>>> --- a/mm/gup.c
>>> +++ b/mm/gup.c
>>> @@ -2739,7 +2739,6 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
>>> {
>>> bool reject_file_backed = false;
>>> struct address_space *mapping;
>>> - bool check_secretmem = false;
>>> unsigned long mapping_flags;
>>>
>>> /*
>>> @@ -2751,14 +2750,6 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
>>
>> Copying some lines the diff didn't contain:
>>
>> /*
>> * If we aren't pinning then no problematic write can occur. A long term
>> * pin is the most egregious case so this is the one we disallow.
>> */
>> if ((flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) ==
>> (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE))
>>
>> If we're pinning, can we already return true here? IIUC this function
>> is passed a folio that is file-backed, and the check if (!mapping) is
>> just there to catch the case where the mapping got truncated.
>
> I have to admit that I am not comfortable with removing this check,
> unless someone says it's certainly alright.
>
Perhaps David can help here, David last changed this in
f002882ca369aba3eece5006f3346ccf75ede7c5 (mm: merge folio_is_secretmem()
and folio_fast_pin_allowed() into gup_fast_folio_allowed()) from return
true to check_secretmem = true :)
>>
>> Or should we wait for the check where the mapping got truncated? If so,
>> then maybe we can move this "are we pinning" check to after this check
>> and remove the reject_file_backed variable?
>
> I can indeed move the pinning check to the end to remove the variable.
> I'd do it in a separate patch.
>
>>
>> /*
>> * The mapping may have been truncated, in any case we cannot determine
>> * if this mapping is safe - fall back to slow path to determine how to
>> * proceed.
>> */
>> if (!mapping)
>> return false;
>>
>>
>>> reject_file_backed = true;
>>>
>>> /* We hold a folio reference, so we can safely access folio fields. */
>>> -
>>> - /* secretmem folios are always order-0 folios. */
>>> - if (IS_ENABLED(CONFIG_SECRETMEM) && !folio_test_large(folio))
>>> - check_secretmem = true;
>>> -
>>> - if (!reject_file_backed && !check_secretmem)
>>> - return true;
>>> -
>>> if (WARN_ON_ONCE(folio_test_slab(folio)))
>>> return false;
>>>
>>> @@ -2800,7 +2791,7 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
>>> * At this point, we know the mapping is non-null and points to an
>>> * address_space object.
>>> */
>>> - if (check_secretmem && secretmem_mapping(mapping))
>>> + if (secretmem_mapping(mapping))
>>> return false;
>>> /* The only remaining allowed file system is shmem. */
>>> return !reject_file_backed || shmem_mapping(mapping);
>>> --
>>> 2.50.1
Powered by blists - more mailing lists