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b=meKsfZG7Mz03e3WAkn/HPFLDZOmTDBOKCSQFOevvDp5edvLDhQ5ZaQhN18w6YvQF+ bI32Gu8m6ecxnGvhRxpwRzPZWTvaaVVzIycqlEjadO0UbBx+XZYFIILDfRDueqoTog k2NgYqmYDC1lNbevKho3uOIbztKbXULKniiln52RmnIiXcqjXnG+5k/GdY2kZB9ILm cz+Nis4gfBaA9P8uAeQVKFWF2cIx27KqN2LOEooqj+EKwkMqGvcjSfWkxxn4R9zvTY H7WKDOR11p0ysMu3+uD4m8LpHBqBHzW3fjjYUSvDCcRfuo1DDrMiodMi70noRcLb0n 0IkidHKKgSxUw== Message-ID: Date: Fri, 6 Mar 2026 16:17:29 +0100 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> <40bd6f9b-d5c0-4844-81bc-d221cd9b058f@kernel.org> <38deb26a-918c-4743-b35f-92a1330dbf40@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 X-Rspamd-Queue-Id: 78F8B1C0004 X-Rspamd-Server: rspam07 X-Stat-Signature: pop9z73jb313d1ngtbz5fydspdrkwi7j X-Rspam-User: X-HE-Tag: 1772810277-216342 X-HE-Meta: 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 5ziFa71S UvtPMMalW4knA6/MfEbQ5li6hDtkbBI3tXEGYGQwH2r6RQFCvSmewtLDGDKWoWJ/RVsXp4k7a0/XJntww4gs4pQJl4UCl3/LrmvSF89XeKlG86IhgZTSdzHfvH1hW7ZNq0eWo6E2WnySTHCqpfsBQNI7nnfCpRAj38YOutxuIHiNj+KZUxj751YK41QLVl6XRVPb77/j+CAR5UEnyQjfgx7OHLPZWdimuzTPQvCyZcoXr8ImgBCLGYiau/TR7ylyggSHM1UZFxSFafpMvweeeY70N2QKJMrOe2apk/lY3QH/e/NSRQK+c7k3h9IECoxV/irvtjUcCLHJWtgtrk6XvyC0HdV7W8MZGvF8Kdg9pNUOkLxutaPLL1bCOrJuXs49JEqrbPbsqMM7OVPSxgx93RTjzYxhBy7wSjmAreiZ6QwbAGF8wRZeEATUwMxBbAX09h6Mv/I4tHHbtZYZv4sFGOQHhj79JgVZbw9JnNn4h595cve0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/6/26 15:48, Nikita Kalyazin wrote: > > > On 06/03/2026 14:17, David Hildenbrand (Arm) wrote: >> On 3/6/26 13:48, Nikita Kalyazin wrote: >>> >>> >>> >>> Will update, thanks. >>> >>> >>> Absolutely! >>> >>> >>> 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. > > Yeah, that's unfortunately the status quo as pointed by Aneesh [1] > > [1] https://lore.kernel.org/kvm/yq5ajz07czvz.fsf@kernel.org/ > >> >> Take a look at secretmem_fault(), where we do an unconditional >> flush_tlb_kernel_range(). >> >> Do we end up double-flushing in that case? > > Yes, looks like that.  I'll remove the explicit flush and rely on > folio_zap_direct_map(). > >> >>> 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. > > I believe Dave meant to address that with folio_{zap,restore} > _direct_map() [2]. > > [2] https://lore.kernel.org/kvm/9409531b-589b-4a54- > b122-06a3cf0846f3@intel.com/ > >> >> 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. > > I'd be inclined to know what arch maintainers think because I don't have > a strong opinion on that. You could also just perform a double flush, and let people that implemented a _noflush() to perform a flush optimize that later. I mean, that's what secretmem did :) -- Cheers, David