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([2001:b07:6468:f312:9af8:e5f5:7516:fa89]) by smtp.googlemail.com with ESMTPSA id y13-20020a170906470d00b0099bd1a78ef5sm957651ejq.74.2023.11.02.03.32.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Nov 2023 03:32:39 -0700 (PDT) Message-ID: Date: Thu, 2 Nov 2023 11:32:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 13/35] KVM: Introduce per-page memory attributes To: "Huang, Kai" , "viro@zeniv.linux.org.uk" , "aou@eecs.berkeley.edu" , "Christopherson,, Sean" , "brauner@kernel.org" , "oliver.upton@linux.dev" , "chenhuacai@kernel.org" , "paul.walmsley@sifive.com" , "palmer@dabbelt.com" , "maz@kernel.org" , "mpe@ellerman.id.au" , "willy@infradead.org" , "anup@brainfault.org" , "akpm@linux-foundation.org" Cc: "Li, Xiaoyao" , "kvm-riscv@lists.infradead.org" , "mic@digikod.net" , "liam.merwick@oracle.com" , "kvm@vger.kernel.org" , "Yamahata, Isaku" , "kirill.shutemov@linux.intel.com" , "david@redhat.com" , "tabba@google.com" , "amoorthy@google.com" , "linuxppc-dev@lists.ozlabs.org" , "michael.roth@amd.com" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-riscv@lists.infradead.org" , "chao.p.peng@linux.intel.com" , "linux-mips@vger.kernel.org" , "Annapurve, Vishal" , "vbabka@suse.cz" , "mail@maciej.szmigiero.name" , "yu.c.zhang@linux.intel.com" , "qperret@google.com" , "dmatlack@google.com" , "Xu, Yilun" , "isaku.yamahata@gmail.com" , "ackerleytng@google.com" , "jarkko@kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mm@kvack.org" , "Wang, Wei W" References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-14-seanjc@google.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 92029100013 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: sppktm4x9qmqprwz7ya7yewrn98f988q X-HE-Tag: 1698921163-345036 X-HE-Meta: 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 4ZbrI13i 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/2/23 04:01, Huang, Kai wrote: > On Fri, 2023-10-27 at 11:21 -0700, Sean Christopherson wrote: >> From: Chao Peng >> >> In confidential computing usages, whether a page is private or shared is >> necessary information for KVM to perform operations like page fault >> handling, page zapping etc. There are other potential use cases for >> per-page memory attributes, e.g. to make memory read-only (or no-exec, >> or exec-only, etc.) without having to modify memslots. >> >> Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow >> userspace to operate on the per-page memory attributes. >> - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to >> a guest memory range. >> - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported >> memory attributes. >> >> Use an xarray to store the per-page attributes internally, with a naive, >> not fully optimized implementation, i.e. prioritize correctness over >> performance for the initial implementation. >> >> Use bit 3 for the PRIVATE attribute so that KVM can use bits 0-2 for RWX >> attributes/protections in the future, e.g. to give userspace fine-grained >> control over read, write, and execute protections for guest memory. >> >> Provide arch hooks for handling attribute changes before and after common >> code sets the new attributes, e.g. x86 will use the "pre" hook to zap all >> relevant mappings, and the "post" hook to track whether or not hugepages >> can be used to map the range. >> >> To simplify the implementation wrap the entire sequence with >> kvm_mmu_invalidate_{begin,end}() even though the operation isn't strictly >> guaranteed to be an invalidation. For the initial use case, x86 *will* >> always invalidate memory, and preventing arch code from creating new >> mappings while the attributes are in flux makes it much easier to reason >> about the correctness of consuming attributes. >> >> It's possible that future usages may not require an invalidation, e.g. >> if KVM ends up supporting RWX protections and userspace grants _more_ >> protections, but again opt for simplicity and punt optimizations to >> if/when they are needed. >> >> Suggested-by: Sean Christopherson >> Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com >> Cc: Fuad Tabba >> Cc: Xu Yilun >> Cc: Mickaël Salaün >> Signed-off-by: Chao Peng >> Co-developed-by: Sean Christopherson >> Signed-off-by: Sean Christopherson >> > > [...] > >> +Note, there is no "get" API. Userspace is responsible for explicitly tracking >> +the state of a gfn/page as needed. >> + >> > > [...] > >> >> +#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES >> +static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn) >> +{ >> + return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)); >> +} > > Only call xa_to_value() when xa_load() returns !NULL? This xarray does not store a pointer, therefore xa_load() actually returns an integer that is tagged with 1 in the low bit: static inline unsigned long xa_to_value(const void *entry) { return (unsigned long)entry >> 1; } Returning zero for an empty entry is okay, so the result of xa_load() can be used directly. >> + >> +bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end, >> + unsigned long attrs); > > Seems it's not immediately clear why this function is needed in this patch, > especially when you said there is no "get" API above. Add some material to > changelog? It's used by later patches; even without a "get" API, it's a pretty fundamental functionality. >> +bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm, >> + struct kvm_gfn_range *range); >> +bool kvm_arch_post_set_memory_attributes(struct kvm *kvm, >> + struct kvm_gfn_range *range); > > Looks if this Kconfig is on, the above two arch hooks won't have implementation. > > Is it better to have two __weak empty versions here in this patch? > > Anyway, from the changelog it seems it's not mandatory for some ARCH to provide > the above two if one wants to turn this on, i.e., the two hooks can be empty and > the ARCH can just use the __weak version. I think this can be added by the first arch that needs memory attributes and also doesn't need one of these hooks. Or perhaps the x86 kvm_arch_pre_set_memory_attributes() could be made generic and thus that would be the __weak version. It's too early to tell, so it's better to leave the implementation to the architectures for now. Paolo