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Fri, 16 Jan 2026 14:56:02 +0000 (UTC) X-Farcaster-Flow-ID: 260b6298-10cb-4eed-9151-e85b598fcfcc Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUA002.ant.amazon.com (10.252.50.124) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Fri, 16 Jan 2026 14:56:01 +0000 Received: from [192.168.12.13] (10.106.82.9) by EX19D005EUB003.ant.amazon.com (10.252.51.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Fri, 16 Jan 2026 14:55:57 +0000 Message-ID: <6b50a83e-acd7-4db3-ae9b-015ffad4f615@amazon.com> Date: Fri, 16 Jan 2026 14:55:56 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v9 02/13] mm/gup: drop secretmem optimization from gup_fast_folio_allowed To: Ackerley Tng , "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" References: <20260114134510.1835-1-kalyazin@amazon.com> <20260114134510.1835-3-kalyazin@amazon.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; 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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. > > 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