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charset=UTF-8 Date: Fri, 26 Jun 2026 14:45:45 +0000 Message-Id: Cc: "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" , "pbonzini@redhat.com" , "corbet@lwn.net" , "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" , "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" , "borntraeger@linux.ibm.com" , "chenhuacai@kernel.org" , "baolu.lu@linux.intel.com" , "dev.jain@arm.com" , "palmer@dabbelt.com" , "pjw@kernel.org" , "shijie@os.amperecomputing.com" , "thuth@redhat.com" , "yang@os.amperecomputing.com" , "Liam.Howlett@oracle.com" , "zhengqi.arch@bytedance.com" , "lenb@kernel.org" , "pavel@kernel.org" , "yangyicong@hisilicon.com" , "vannapurve@google.com" , "jackmanb@google.com" , "patrick.roy@linux.dev" , "Itazuri, Takahiro" Subject: Re: [PATCH v12 09/16] KVM: arm64: define kvm_arch_gmem_supports_no_direct_map() X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: "Brendan Jackman" To: "Marc Zyngier" , "Kalyazin, Nikita" References: <20260410151746.61150-1-kalyazin@amazon.com> <20260410151746.61150-10-kalyazin@amazon.com> <86fr4o1ceu.wl-maz@kernel.org> In-Reply-To: <86fr4o1ceu.wl-maz@kernel.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 82DFC1C0009 X-Rspam-User: X-Stat-Signature: tjru3hiy6crtsn7e6eaimm33nncyfm67 X-HE-Tag: 1782485158-592982 X-HE-Meta: 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 m9ioODGW JSWhoeE86H9goWJQOk347PB5t/s4XQMDsj9UfiOkSRQVJzFIZpnTEGeKvRX/5AC+CbHH1j38nnYgAHtlNCU4nlucDaDzM2QbcEhnmita8PqgPZLtiiGlI3W1llXuGrhby5v3WWC2si2JARAr1P2tVyGIeHJ2rHvIwymZ2pR2PgeLRubxKMMpwz3gVPZLWh7PC6AHs1oWCMSSXsgH3ukCgHEUlmBmczhWbDOx1pxggrngWP8fQEzfj3UdMeZKArf2QcHGH0Qd88GLPX2fWXUbo1obqdiBI46fsbnBiRrCpvYK7x0tOEDaTim6H3GGtBy1evy79w5H00kIrCOJGs2fL3dlO13/knYpkHZl4bh17hQsH0K2EU6h7qJ8FW+7j2LqxdsOLCNROVxYvTjM36fhNgWktXNmP6Op1CmWvgNQACpenZJM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue Apr 21, 2026 at 4:55 PM UTC, Marc Zyngier wrote: > On Fri, 10 Apr 2026 16:19:24 +0100, > "Kalyazin, Nikita" wrote: >>=20 >> From: Patrick Roy >>=20 >> Support for GUEST_MEMFD_FLAG_NO_DIRECT_MAP on arm64 depends on 1) direct >> map manipulations at 4k granularity being possible, and 2) FEAT_S2FWB. >>=20 >> 1) is met whenever the direct map is set up at 4k granularity (e.g. not >> with huge/gigantic pages) at boottime, as due to ARM's >> break-before-make semantics, breaking huge mappings into 4k mappings in >> the direct map is not possible (BBM would require temporary invalidation >> of the entire huge mapping, even if only a 4k subrange should be zapped, >> which will probably crash the kernel). However, the current default for >> rodata_full is true, which forces a 4k direct map. > > Where is this 4kB requirement enforced? Or is it that you means > "PAGE_SIZE"? Yeah I believe this means PAGE_SIZE and that it's effectively enforced by checking can_set_direct_map() in kvm_arch_gmem_supports_no_direct_map().