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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QyTmHOD4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QyTmHOD4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6FC83C4CEF7; Fri, 6 Mar 2026 14:17:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772806657; bh=kDJQMMVjroxoqrKJpgts6ufp43e8NaCEQtf/5Qs5cB4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=QyTmHOD4CzeDxFBjYfTfC6aL3PiHmprBUm5aDWYj20TxoXCHTJX8pGTIdNei8th5h tvRNSvoY2RpvRn1wE761+UsErbXxvMe0nwGgq4nu2Kwo3msE2iwC9NYuM+gMRydmfa Dy+ac+sBOxKQLGyi72NUoxWG2kAcat6b+aUTOB2pEBeuOstaacg4nHN8PPdxbAft+G eTaUxKsXNioJoJdnZRtzOookjps1JooJOaepfmNUXz08uHBqWqzXFLdzJXzhWRatcv VSEPqivLxU9hODu3+CF/kdtVEHRcgG2my++WMm71t7osmCoBM2JKJjTCv+UoMspcG0 zy9nbkCf2BrCg== Message-ID: <40bd6f9b-d5c0-4844-81bc-d221cd9b058f@kernel.org> Date: Fri, 6 Mar 2026 15:17:03 +0100 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 02/15] set_memory: add folio_{zap, restore}_direct_map helpers 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@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@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" , "ackerleytng@google.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" , "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" , "Cali, Marco" References: <20260126164445.11867-1-kalyazin@amazon.com> <20260126164445.11867-3-kalyazin@amazon.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 3/6/26 13:48, Nikita Kalyazin wrote: > > > On 05/03/2026 17:34, David Hildenbrand (Arm) wrote: >> On 1/26/26 17:47, Kalyazin, Nikita wrote: >>> From: Nikita Kalyazin >>> >>> These allow guest_memfd to remove its memory from the direct map. >>> Only implement them for architectures that have direct map. >>> In folio_zap_direct_map(), flush TLB on architectures where >>> set_direct_map_valid_noflush() does not flush it internally. >> >> "Let's provide folio_{zap,restore}_direct_map helpers as preparation for >> supporting removal of the direct map for guest_memfd folios. ... > > Will update, thanks. > >> >>> >>> The new helpers need to be accessible to KVM on architectures that >>> support guest_memfd (x86 and arm64).  Since arm64 does not support >>> building KVM as a module, only export them on x86. >>> >>> Direct map removal gives guest_memfd the same protection that >>> memfd_secret does, such as hardening against Spectre-like attacks >>> through in-kernel gadgets. >> >> Would it be possible to convert mm/secretmem.c as well? >> >> There, we use >> >>          set_direct_map_invalid_noflush(folio_page(folio, 0)); >> >> and >> >>          set_direct_map_default_noflush(folio_page(folio, 0)); >> >> Which is a bit different to below code. At least looking at the x86 >> variants, I wonder why we don't simply use >> set_direct_map_valid_noflush(). >> >> >> If so, can you add a patch to do the conversion, pleeeeassse ? :) > > Absolutely! > >> >>> >>> Reviewed-by: Ackerley Tng >>> Signed-off-by: Nikita Kalyazin >>> --- >>>   arch/arm64/include/asm/set_memory.h     |  2 ++ >>>   arch/arm64/mm/pageattr.c                | 12 ++++++++++++ >>>   arch/loongarch/include/asm/set_memory.h |  2 ++ >>>   arch/loongarch/mm/pageattr.c            | 12 ++++++++++++ >>>   arch/riscv/include/asm/set_memory.h     |  2 ++ >>>   arch/riscv/mm/pageattr.c                | 12 ++++++++++++ >>>   arch/s390/include/asm/set_memory.h      |  2 ++ >>>   arch/s390/mm/pageattr.c                 | 12 ++++++++++++ >>>   arch/x86/include/asm/set_memory.h       |  2 ++ >>>   arch/x86/mm/pat/set_memory.c            | 20 ++++++++++++++++++++ >>>   include/linux/set_memory.h              | 10 ++++++++++ >>>   11 files changed, 88 insertions(+) >>> >>> diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/ >>> include/asm/set_memory.h >>> index c71a2a6812c4..49fd54f3c265 100644 >>> --- a/arch/arm64/include/asm/set_memory.h >>> +++ b/arch/arm64/include/asm/set_memory.h >>> @@ -15,6 +15,8 @@ int set_direct_map_invalid_noflush(const void *addr); >>>   int set_direct_map_default_noflush(const void *addr); >>>   int set_direct_map_valid_noflush(const void *addr, unsigned long >>> numpages, >>>                                 bool valid); >>> +int folio_zap_direct_map(struct folio *folio); >>> +int folio_restore_direct_map(struct folio *folio); >>>   bool kernel_page_present(struct page *page); >>> >>>   int set_memory_encrypted(unsigned long addr, int numpages); >>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c >>> index e2bdc3c1f992..0b88b0344499 100644 >>> --- a/arch/arm64/mm/pageattr.c >>> +++ b/arch/arm64/mm/pageattr.c >>> @@ -356,6 +356,18 @@ int set_direct_map_valid_noflush(const void >>> *addr, unsigned long numpages, >>>        return set_memory_valid((unsigned long)addr, numpages, valid); >>>   } >>> >>> +int folio_zap_direct_map(struct folio *folio) >>> +{ >>> +     return set_direct_map_valid_noflush(folio_address(folio), >>> +                                         folio_nr_pages(folio), false); >>> +} >>> + >>> +int folio_restore_direct_map(struct folio *folio) >>> +{ >>> +     return set_direct_map_valid_noflush(folio_address(folio), >>> +                                         folio_nr_pages(folio), true); >>> +} >> >> Is there a good reason why we cannot have two generic inline functions >> that simply call set_direct_map_valid_noflush() ? >> >> Is it because of some flushing behavior? (which we could figure out) > > Yes, on x86 we need an explicit flush.  Other architectures deal with it > internally.  So, we call a _noflush function and it performs a ... flush. What. Take a look at secretmem_fault(), where we do an unconditional flush_tlb_kernel_range(). Do we end up double-flushing in that case? > Do you propose a bespoke implementation for x86 and a > "generic" one for others? We have to find a way to have a single set of functions for all archs that support directmap removal. One option might be to have some indication from the architecture that no flush_tlb_kernel_range() is required. Could be a config option or some simple helper function. -- Cheers, David