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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a8211b74c8sm3504720a91.0.2026.10.05.23.16.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 05 Oct 2026 23:16:47 -0700 (PDT) Message-ID: <6bd785aa-4693-407d-b70a-39b1d0eda63e@redhat.com> Date: Tue, 6 Oct 2026 16:16:37 +1000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v22 23/23] KVM: arm64: CCA: Control user register access for Realms To: Suzuki K Poulose , kvm@vger.kernel.org, kvmarm@lists.linux.dev Cc: maz@kernel.org, will@kernel.org, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, steven.price@arm.com, aneesh.kumar@kernel.org, oupton@kernel.org, joey.gouly@arm.com, tabba@google.com, yuzenghui@huawei.com, linux-coco@lists.linux.dev, gankulkarni@os.amperecomputing.com, sdonthineni@nvidia.com, alpergun@google.com, fj0570is@fujitsu.com, WeiLin.Chang@arm.com, lpieralisi@kernel.org, enju.kohei@fujitsu.com, sudeep.holla@arm.com, jonathan.cameron@oss.qualcomm.com, Jean-Philippe Brucker References: <20261005090754.2140522-1-suzuki.poulose@arm.com> <20261005090754.2140522-24-suzuki.poulose@arm.com> <52e3e45a-751e-40b2-8dd3-3db589ddebee@redhat.com> <7b6ed626-eca4-41f2-ae56-0af59a931b29@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <7b6ed626-eca4-41f2-ae56-0af59a931b29@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/6/26 4:01 PM, Suzuki K Poulose wrote: > On 06/10/2026 06:47, Gavin Shan wrote: >> On 10/5/26 7:07 PM, Suzuki K Poulose wrote: >>> From: Jean-Philippe Brucker >>> >>> The RMM restricts the access to the register states that the host can >>> read/modify for a given Realm. >>> >>> e.g., At VCPU creation, can modify GPRS (x0-x30) and PC. >>>        While servicing SMCCC calls via RSI_HOST_CALL or servicing PSCI >>>        requests. >>>        MMIO emulation in the unprotected space. >>> >>> Additionally we use the sysreg configuration to advertise/configure the >>> following Realm parameters, which are required before the Realm Descriptor >>> is created: >>>   - SVE Vector Length >>>   - Number of HW Breakpoints/Watchpoints >>>   - PMU Counters. >>> >>> Thus KVM also additionally allows access to ID_AA64DFR0_EL1 and SVE_VLS for >>> the configuration of Realm creation parameters. We don't support PMUs for >>> the Realm VMs yet, so PMCR is not exposed. >>> >>> The RMM makes similar restrictions for reading of the guest's registers >>> (this is *confidential* compute after all), however we don't impose the >>> restriction here. This allows the VMM to read (stale) values from the >>> registers which might be useful to read back the initial values even if >>> the RMM doesn't provide the latest version. For migration of a realm VM, >>> a new interface will be needed so that the VMM can receive an >>> (encrypted) blob of the VM's state. >>> >>> Reflect the above in KVM_GET_REG_LIST, KVM_SET_ONE_REG calls. > >>>   static int core_reg_size_from_offset(const struct kvm_vcpu *vcpu, u64 off) >>>   { >>>       int size; >>> @@ -553,6 +572,9 @@ static int copy_core_reg_indices(const struct kvm_vcpu *vcpu, >>>           u64 reg = KVM_REG_ARM64 | KVM_REG_ARM_CORE | i; >>>           int size = core_reg_size_from_offset(vcpu, i); >>> +        if (vcpu_is_rec(vcpu) && !kvm_realm_validate_core_reg(i)) >>> +            continue; >>> + >>>           if (size < 0) >>>               continue; >>> @@ -598,6 +620,9 @@ static unsigned long num_sve_regs(const struct kvm_vcpu *vcpu) >>>       if (!vcpu_has_sve(vcpu)) >>>           return 0; >>> +    if (kvm_vm_is_realm(vcpu->kvm)) >>> +        return 1; /* KVM_REG_ARM64_SVE_VLS */ >>> + >>>       if (!kvm_arm_vcpu_sve_finalized(vcpu)) >>>           return 1; /* KVM_REG_ARM64_SVE_VLS */ >>> >> >> Aren't above two checks conflicting to each other? > > Do they? We allow SVE_VLS only for the Realms and we allow that > before the vCPUs are finalized. For normal VMs, depending on > whether the vcpus are finalized, we either send 1 or the full list. > num_sve_regs() can be called for 3 cases: (a) non-finalized RECs; (b) finalized RECs; (c) Other finalized vCPUs, correct? "if (kvm_vm_is_realm(vcpu->kvm))", which would be "if (vcpu_is_rec(vcpu))", covers (a) and (b). We needn't the excessive check "if (!kvm_arm_vcpu_sve_finalized(vcpu))". So the check would be something as below after this series is applied: /* * KVM_REG_ARM64_SVE_VLS is visible on realm vCPU no matter if it * has been finalized. */ if (vcpu_is_rec(vcpu)) return 1; This check "if (vcpu_is_rec(vcpu))" belongs to PATCH[22]. Hope I make myself clear this time :) >> >>> @@ -625,6 +650,10 @@ static int copy_sve_reg_indices(const struct kvm_vcpu *vcpu, >>>           return -EFAULT; >>>       ++num_regs; >>> +    /* For Realms only support SVE_VLS */ >>> +    if (kvm_vm_is_realm(vcpu->kvm)) >>> +        return num_regs; >>> + >>>       if (!kvm_arm_vcpu_sve_finalized(vcpu)) >>>           return num_regs; >> >> Same question here. > > As above. > > Suzuki Thanks, Gavin