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Wed, 21 Jan 2026 16:20:20 -0800 (PST) Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Wed, 21 Jan 2026 16:20:19 -0800 Received: from 176938342045 named unknown by gmailapi.google.com with HTTPREST; Wed, 21 Jan 2026 16:20:19 -0800 From: Ackerley Tng In-Reply-To: <6b50a83e-acd7-4db3-ae9b-015ffad4f615@amazon.com> References: <20260114134510.1835-1-kalyazin@amazon.com> <20260114134510.1835-3-kalyazin@amazon.com> <6b50a83e-acd7-4db3-ae9b-015ffad4f615@amazon.com> MIME-Version: 1.0 Date: Wed, 21 Jan 2026 16:20:19 -0800 X-Gm-Features: AZwV_Qi8Ad3srMrd8WYJ_YHR6Nmvzc-hfHPfYm40mDZ1I3o7aAQCl-nKoDyQfts Message-ID: Subject: Re: [PATCH v9 02/13] mm/gup: drop secretmem optimization from gup_fast_folio_allowed To: kalyazin@amazon.com, "Kalyazin, Nikita" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.linux.dev" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "kernel@xen0n.name" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "loongarch@lists.linux.dev" Cc: "pbonzini@redhat.com" , "corbet@lwn.net" , "maz@kernel.org" , "oupton@kernel.org" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "seanjc@google.com" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "luto@kernel.org" , "peterz@infradead.org" , "willy@infradead.org" , "akpm@linux-foundation.org" , "david@kernel.org" , "lorenzo.stoakes@oracle.com" , "Liam.Howlett@oracle.com" , "vbabka@suse.cz" , "rppt@kernel.org" , "surenb@google.com" , "mhocko@suse.com" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "martin.lau@linux.dev" , "eddyz87@gmail.com" , "song@kernel.org" , "yonghong.song@linux.dev" , "john.fastabend@gmail.com" , "kpsingh@kernel.org" , "sdf@fomichev.me" , "haoluo@google.com" , "jolsa@kernel.org" , "jgg@ziepe.ca" , "jhubbard@nvidia.com" , "peterx@redhat.com" , "jannh@google.com" , "pfalcato@suse.de" , "shuah@kernel.org" , "riel@surriel.com" , "ryan.roberts@arm.com" , "jgross@suse.com" , "yu-cheng.yu@intel.com" , "kas@kernel.org" , "coxu@redhat.com" , "kevin.brodsky@arm.com" , "maobibo@loongson.cn" , "prsampat@amd.com" , "mlevitsk@redhat.com" , "jmattson@google.com" , "jthoughton@google.com" , "agordeev@linux.ibm.com" , "alex@ghiti.fr" , "aou@eecs.berkeley.edu" , "borntraeger@linux.ibm.com" , "chenhuacai@kernel.org" , "dev.jain@arm.com" , "gor@linux.ibm.com" , "hca@linux.ibm.com" , "Jonathan.Cameron@huawei.com" , "palmer@dabbelt.com" , "pjw@kernel.org" , "shijie@os.amperecomputing.com" , "svens@linux.ibm.com" , "thuth@redhat.com" , "wyihan@google.com" , "yang@os.amperecomputing.com" , "vannapurve@google.com" , "jackmanb@google.com" , "aneesh.kumar@kernel.org" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Itazuri, Takahiro" , "Manwaring, Derek" , "Cali, Marco" Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: s3r6y8pm573jokk48ty4r163gk3jtn7b X-Rspamd-Queue-Id: D1A144000B X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1769041223-849890 X-HE-Meta: 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 SVQp1AKL 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Nikita Kalyazin writes: > On 15/01/2026 21:40, Ackerley Tng wrote: >> "Kalyazin, Nikita" writes: >> >>> From: Patrick Roy >>> >>> 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 >>> Acked-by: Vlastimil Babka >>> Signed-off-by: Nikita Kalyazin >>> --- >>> 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