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Fri, 10 Apr 2026 15:27:22 +0000 (UTC) X-Farcaster-Flow-ID: 0adabb76-9e17-4c0c-bcfb-c40d0e8bf47b Received: from EX19D027UEC003.ant.amazon.com (10.252.137.250) by EX19MTAUEA001.ant.amazon.com (10.252.134.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 10 Apr 2026 15:27:22 +0000 Received: from [192.168.12.97] (10.106.82.30) by EX19D027UEC003.ant.amazon.com (10.252.137.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 10 Apr 2026 15:27:09 +0000 Message-ID: Date: Fri, 10 Apr 2026 16:27:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v11 04/16] mm/gup: drop secretmem optimization from gup_fast_folio_allowed To: "David Hildenbrand (Arm)" , "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" , "linux-pm@vger.kernel.org" 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@kernel.org" , "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" , "lorenzo.stoakes@oracle.com" , "vbabka@kernel.org" , "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" , "skhan@linuxfoundation.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" , "ackerleytng@google.com" , "yosry@kernel.org" , "ajones@ventanamicro.com" , "maobibo@loongson.cn" , "tabba@google.com" , "prsampat@amd.com" , "wu.fei9@sanechips.com.cn" , "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" , "palmer@dabbelt.com" , "pjw@kernel.org" , "shijie@os.amperecomputing.com" , "svens@linux.ibm.com" , "thuth@redhat.com" , "wyihan@google.com" , "yang@os.amperecomputing.com" , "Jonathan.Cameron@huawei.com" , "Liam.Howlett@oracle.com" , "urezki@gmail.com" , "zhengqi.arch@bytedance.com" , "gerald.schaefer@linux.ibm.com" , "jiayuan.chen@shopee.com" , "lenb@kernel.org" , "osalvador@suse.de" , "pavel@kernel.org" , "rafael@kernel.org" , "vannapurve@google.com" , "jackmanb@google.com" , "aneesh.kumar@kernel.org" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Itazuri, Takahiro" , "Manwaring, Derek" , Vlastimil Babka , Dan Williams , Alistair Popple References: <20260317141031.514-1-kalyazin@amazon.com> <20260317141031.514-5-kalyazin@amazon.com> <76f14d3e-c8fb-4380-9d12-2375f199b53f@kernel.org> 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 >> Acked-by: David Hildenbrand (Red Hat) >> 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 8e7dc2c6ee73..5856d35be385 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) >> 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; >> - > > The AI review says that this will force all small folios through the > mapping check (which we obviously need later :) ). > > It brings up two cases where page->mapping is not set up: > > 1) ZONE_DEVICE pages (like Device DAX and PCI P2PDMA) > > 2) large shmem folios in the swap cache > > > 2) doesn't make sense, because the folio cannot be mapped in user space > when that happens. > > I am also skeptical about 1), especially as large folios are also > supported for device dax and would be problematic here. > __dev_dax_pte_fault() clearly sets folio->mapping through dax_set_mapping(). > > > If 1) is ever a case we could allow them by checking for > folio_is_zone_device(). But I am not sure if that is really required. > Sounds weird. I went ahead and added a check for folio_is_zone_device(). > > > -- > Cheers, > > David