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Fri, 10 Apr 2026 15:26:12 +0000 (UTC) X-Farcaster-Flow-ID: 7fbceef4-e2e0-48cc-89a3-9e29bae5d585 Received: from EX19D027UEC003.ant.amazon.com (10.252.137.250) by EX19MTAUEB002.ant.amazon.com (10.252.135.47) 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 15:26:12 +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 15:25:59 +0000 Message-ID: <532481d6-f137-4666-b2e3-77aa1b5c8177@amazon.com> Date: Fri, 10 Apr 2026 16:25:57 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v11 02/16] set_memory: add folio_{zap, restore}_direct_map helpers 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" , "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" , "david@kernel.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" , "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" References: <20260317141031.514-1-kalyazin@amazon.com> <20260317141031.514-3-kalyazin@amazon.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; keydata= xjMEY+ZIvRYJKwYBBAHaRw8BAQdA9FwYskD/5BFmiiTgktstviS9svHeszG2JfIkUqjxf+/N JU5pa2l0YSBLYWx5YXppbiA8a2FseWF6aW5AYW1hem9uLmNvbT7CjwQTFggANxYhBGhhGDEy BjLQwD9FsK+SyiCpmmTzBQJp2NfjBQkGQlIzAhsDBAsJCAcFFQgJCgsFFgIDAQAACgkQr5LK IKmaZPPNDAEAvsw8vEWj8ArWQ1QJNufjrvobU/cE8MLKdBxbSE8CyZQA/0BldKxNAtAwG4qw wCLxsZ5vBL3Zkh/PdvtFCj/VGscGzjgEY+ZIvRIKKwYBBAGXVQEFAQEHQCqd7/nb2tb36vZt ubg1iBLCSDctMlKHsQTp7wCnEc4RAwEIB8J+BBgWCAAmFiEEaGEYMTIGMtDAP0Wwr5LKIKma ZPMFAmnY1+MFCQZCUjMCGwwACgkQr5LKIKmaZPPQKgD/f3FtERbJ+LYHLSG/ZbLNAOLngUlQ qo5VfIyJOzeLzC0BAP2PIUFIHo7vmia/PXEmT+ve4c5rx+EkH/Dx1GRpjWoI In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: EX19D003EUA001.ant.amazon.com (10.252.50.31) To EX19D027UEC003.ant.amazon.com (10.252.137.250) On 23/03/2026 18:43, Ackerley Tng wrote: > "Kalyazin, Nikita" writes: > >> From: Nikita Kalyazin >> >> Let's provide folio_{zap,restore}_direct_map helpers as preparation for >> supporting removal of the direct map for guest_memfd folios. >> In folio_zap_direct_map(), flush TLB to make sure the data is not >> accessible. >> >> The new helpers need to be accessible to KVM on architectures that >> support guest_memfd (x86 and arm64). >> >> Direct map removal gives guest_memfd the same protection that >> memfd_secret does, such as hardening against Spectre-like attacks >> through in-kernel gadgets. >> >> Signed-off-by: Nikita Kalyazin >> --- >> include/linux/set_memory.h | 13 ++++++++++++ >> mm/memory.c | 42 ++++++++++++++++++++++++++++++++++++++ >> 2 files changed, 55 insertions(+) >> >> diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h >> index 1a2563f525fc..24caea2931f9 100644 >> --- a/include/linux/set_memory.h >> +++ b/include/linux/set_memory.h >> @@ -41,6 +41,15 @@ static inline int set_direct_map_valid_noflush(const void *addr, >> return 0; >> } >> >> +static inline int folio_zap_direct_map(struct folio *folio) >> +{ >> + return 0; >> +} >> + >> +static inline void folio_restore_direct_map(struct folio *folio) >> +{ >> +} >> + >> static inline bool kernel_page_present(struct page *page) >> { >> return true; >> @@ -57,6 +66,10 @@ static inline bool can_set_direct_map(void) >> } >> #define can_set_direct_map can_set_direct_map >> #endif >> + >> +int folio_zap_direct_map(struct folio *folio); >> +void folio_restore_direct_map(struct folio *folio); >> + >> #endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */ >> >> #ifdef CONFIG_X86_64 >> diff --git a/mm/memory.c b/mm/memory.c >> index 07778814b4a8..cab6bb237fc0 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -78,6 +78,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> >> @@ -7478,3 +7479,44 @@ void vma_pgtable_walk_end(struct vm_area_struct *vma) >> if (is_vm_hugetlb_page(vma)) >> hugetlb_vma_unlock_read(vma); >> } >> + >> +#ifdef CONFIG_ARCH_HAS_SET_DIRECT_MAP >> +/** >> + * folio_zap_direct_map - remove a folio from the kernel direct map >> + * @folio: folio to remove from the direct map >> + * >> + * Removes the folio from the kernel direct map and flushes the TLB. This may >> + * require splitting huge pages in the direct map, which can fail due to memory >> + * allocation. >> + * >> + * Return: 0 on success, or a negative error code on failure. >> + */ >> +int folio_zap_direct_map(struct folio *folio) >> +{ >> + const void *addr = folio_address(folio); >> + int ret; >> + >> + ret = set_direct_map_valid_noflush(addr, folio_nr_pages(folio), false); >> + flush_tlb_kernel_range((unsigned long)addr, >> + (unsigned long)addr + folio_size(folio)); >> + >> + return ret; >> +} >> +EXPORT_SYMBOL_FOR_MODULES(folio_zap_direct_map, "kvm"); >> + >> +/** >> + * folio_restore_direct_map - restore the kernel direct map entry for a folio >> + * @folio: folio whose direct map entry is to be restored >> + * >> + * This may only be called after a prior successful folio_zap_direct_map() on >> + * the same folio. Because the zap will have already split any huge pages in >> + * the direct map, restoration here only updates protection bits and cannot >> + * fail. >> + */ >> +void folio_restore_direct_map(struct folio *folio) >> +{ >> + WARN_ON_ONCE(set_direct_map_valid_noflush(folio_address(folio), >> + folio_nr_pages(folio), true)); >> +} >> +EXPORT_SYMBOL_FOR_MODULES(folio_restore_direct_map, "kvm"); >> +#endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */ >> -- >> 2.50.1 > > Reviewed-by: Ackerley Tng > > I also took a look at Sashiko's [1] comments and I think that the > highmem folio issues should be the responsibility of the caller to > check. Thank you. > > [1] https://sashiko.dev/#/patchset/20260317141031.514-1-kalyazin%40amazon.com