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Tue, 21 Apr 2026 16:55:06 +0000 Date: Tue, 21 Apr 2026 17:55:05 +0100 Message-ID: <86fr4o1ceu.wl-maz@kernel.org> From: Marc Zyngier To: "Kalyazin, Nikita" 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" , "aou@eecs.berkeley.edu" , "borntraeger@linux.ibm.com" , "chenhuacai@kernel.org" , "baolu.lu@linux.intel.com" , "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" , "yang@os.amperecomputing.com" , "Liam.Howlett@oracle.com" , "urezki@gmail.com" , "zhengqi.arch@bytedance.com" , "gerald.schaefer@linux.ibm.com" , "jiayuan.chen@shopee.com" , "lenb@kernel.org" , "pavel@kernel.org" , "rafael@kernel.org" , "yangyicong@hisilicon.com" , "vannapurve@google.com" , "jackmanb@google.com" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Itazuri, Takahiro" , "Manwaring, Derek" Subject: Re: [PATCH v12 09/16] KVM: arm64: define kvm_arch_gmem_supports_no_direct_map() In-Reply-To: <20260410151746.61150-10-kalyazin@amazon.com> References: <20260410151746.61150-1-kalyazin@amazon.com> <20260410151746.61150-10-kalyazin@amazon.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: kalyazin@amazon.co.uk, 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, aou@eecs.berkeley.edu, borntraeger@linux.ibm.com, chenhuacai@kernel.org, baolu.lu@linux.intel.com, 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, yang@os.amperecomputing.com, Liam.Howlett@oracle.com, urezki@gmail.com, zhengqi.arch@bytedance.com, gerald.schaefer@linux.ibm.com, jiayuan.chen@shopee.com, lenb@kernel.org, pavel@kernel.org, rafael@kernel.org, yangyicong@hisilicon.com, vannapurve@google.com, jackmanb@google.com, patrick.roy@linux.dev, jackabt@amazon.co.uk, itazur@amazon.co.uk, derekmn@amazon.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Fri, 10 Apr 2026 16:19:24 +0100, "Kalyazin, Nikita" wrote: > > From: Patrick Roy > > 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. > > 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"? > > 2) is required to allow KVM to elide cache coherency operations when > installing stage 2 page tables, which require the direct map to be > entry for the newly mapped memory to be present (which it will not be, > as guest_memfd would have removed direct map entries in > kvm_gmem_get_pfn()). > > Cc: Will Deacon > Signed-off-by: Patrick Roy > Reviewed-by: David Hildenbrand (Arm) > Signed-off-by: Nikita Kalyazin > --- > arch/arm64/include/asm/kvm_host.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 70cb9cfd760a..fbdd43e7e94e 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -19,6 +19,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1682,6 +1683,18 @@ static __always_inline enum fgt_group_id __fgt_reg_to_group_id(enum vcpu_sysreg > \ > p; \ > }) > +#ifdef CONFIG_KVM_GUEST_MEMFD KVM/arm64 has: select KVM_GUEST_MEMFD > +static inline bool kvm_arch_gmem_supports_no_direct_map(struct kvm *kvm) > +{ > + /* > + * Without FWB, direct map access is needed in kvm_pgtable_stage2_map(), > + * as it calls dcache_clean_inval_poc(). > + */ > + return can_set_direct_map() && cpus_have_final_cap(ARM64_HAS_STAGE2_FWB); > +} > +#define kvm_arch_gmem_supports_no_direct_map kvm_arch_gmem_supports_no_direct_map > +#endif /* CONFIG_KVM_GUEST_MEMFD */ Why is it an inline function? Given that it takes a kvm parameter, I fully expect that you'll have to evaluate this at some point. But since struct kvm cannot be dereferenced in asm/kvm_host.h, it will have to move. How about doing it right now? M. -- Without deviation from the norm, progress is not possible.