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[2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e330d1d2fsm14556705e9.3.2025.09.25.03.25.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 03:25:36 -0700 (PDT) Message-ID: Date: Thu, 25 Sep 2025 12:25:33 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 03/12] mm: introduce AS_NO_DIRECT_MAP To: Patrick Roy Cc: Patrick Roy , pbonzini@redhat.com, corbet@lwn.net, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, 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, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, song@kernel.org, jolsa@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, jannh@google.com, pfalcato@suse.de, shuah@kernel.org, seanjc@google.com, 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, xmarcalx@amazon.co.uk, kalyazin@amazon.co.uk, jackabt@amazon.co.uk, derekmn@amazon.co.uk, tabba@google.com, ackerleytng@google.com References: <20250924151101.2225820-1-patrick.roy@campus.lmu.de> <20250924151101.2225820-4-patrick.roy@campus.lmu.de> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 24.09.25 17:10, Patrick Roy wrote: > From: Patrick Roy > > Add AS_NO_DIRECT_MAP for 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. > > Reject this new type of mappings in all locations that currently reject > secretmem mappings, on the assumption that if secretmem mappings are > rejected somewhere, it is precisely because of an inability to deal with > folios without direct map entries, and then make memfd_secret() use > AS_NO_DIRECT_MAP on its address_space to drop its special > vma_is_secretmem()/secretmem_mapping() checks. > > This drops a 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. > > Use a new flag instead of overloading AS_INACCESSIBLE (which is already > set by guest_memfd) because not all guest_memfd mappings will end up > being direct map removed (e.g. in pKVM setups, parts of guest_memfd that > can be mapped to userspace should also be GUP-able, and generally not > have restrictions on who can access it). > > Acked-by: Mike Rapoport (Microsoft) > Signed-off-by: Patrick Roy > --- I enjoy seeing secretmem special-casing in common code go away. [...] > > /* > @@ -2763,18 +2761,10 @@ 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; > - Losing that optimization is not too bad I guess. Acked-by: David Hildenbrand -- Cheers David / dhildenb