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[84.226.111.173]) by smtp.gmail.com with ESMTPSA id l31sm3314180wms.16.2021.06.08.08.54.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Jun 2021 08:54:04 -0700 (PDT) From: Jean-Philippe Brucker To: maz@kernel.org Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, corbet@lwn.net, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, lorenzo.pieralisi@arm.com, salil.mehta@huawei.com, shameerali.kolothum.thodi@huawei.com, jonathan.cameron@huawei.com, Jean-Philippe Brucker Subject: [RFC PATCH 4/5] KVM: arm64: Pass hypercalls to userspace Date: Tue, 8 Jun 2021 17:48:05 +0200 Message-Id: <20210608154805.216869-5-jean-philippe@linaro.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210608154805.216869-1-jean-philippe@linaro.org> References: <20210608154805.216869-1-jean-philippe@linaro.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Let userspace request to handle all hypercalls that aren't handled by KVM, by setting the KVM_CAP_ARM_HVC_TO_USER capability. With the help of another capability, this will allow userspace to handle PSCI calls. Suggested-by: James Morse Signed-off-by: Jean-Philippe Brucker --- Notes on this implementation: * A similar mechanism was proposed for SDEI some time ago [1]. This RFC generalizes the idea to all hypercalls, since that was suggested on the list [2, 3]. * We're reusing kvm_run.hypercall. I copied x0-x5 into kvm_run.hypercall.args[] to help userspace but I'm tempted to remove this, because: - Most user handlers will need to write results back into the registers (x0-x3 for SMCCC), so if we keep this shortcut we should go all the way and synchronize them on return to kernel. - QEMU doesn't care about this shortcut, it pulls all vcpu regs before handling the call. - SMCCC uses x0-x16 for parameters. x0 does contain the SMCCC function ID and may be useful for fast dispatch, we could keep that plus the immediate number. * Should we add a flag in the kvm_run.hypercall telling whether this is HVC or SMC? Can be added later in those bottom longmode and pad fields. * On top of this we could share with userspace which HVC ranges are available and which ones are handled by KVM. That can actually be added independently, through a vCPU/VM device attribute (which doesn't consume a new ioctl): - userspace issues HAS_ATTR ioctl on the VM fd to query whether this feature is available. - userspace queries the number N of HVC ranges using one GET_ATTR. - userspace passes an array of N ranges using another GET_ATTR. The array is filled and returned by KVM. * Untested for AArch32 guests. [1] https://lore.kernel.org/linux-arm-kernel/20170808164616.25949-12-james.morse@arm.com/ [2] https://lore.kernel.org/linux-arm-kernel/bf7e83f1-c58e-8d65-edd0-d08f27b8b766@arm.com/ [3] https://lore.kernel.org/linux-arm-kernel/f56cf420-affc-35f0-2355-801a924b8a35@arm.com/ --- Documentation/virt/kvm/api.rst | 17 +++++++++++++++-- arch/arm64/include/asm/kvm_host.h | 1 + include/kvm/arm_psci.h | 4 ++++ include/uapi/linux/kvm.h | 1 + arch/arm64/kvm/arm.c | 5 +++++ arch/arm64/kvm/hypercalls.c | 28 +++++++++++++++++++++++++++- 6 files changed, 53 insertions(+), 3 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index e4fe7fb60d5d..3d8c1661e7b2 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5228,8 +5228,12 @@ to the byte array. __u32 pad; } hypercall; -Unused. This was once used for 'hypercall to userspace'. To implement -such functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390). +On x86 this was once used for 'hypercall to userspace'. To implement such +functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390). + +On arm64 it is used for hypercalls, when the KVM_CAP_ARM_HVC_TO_USER capability +is enabled. 'nr' contains the HVC or SMC immediate. 'args' contains registers +x0 - x5. The other parameters are unused. .. note:: KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO. @@ -6894,3 +6898,12 @@ This capability is always enabled. This capability indicates that the KVM virtual PTP service is supported in the host. A VMM can check whether the service is available to the guest on migration. + +8.33 KVM_CAP_ARM_HVC_TO_USER +---------------------------- + +:Architecture: arm64 + +This capability indicates that KVM can pass unhandled hypercalls to userspace, +if the VMM enables it. Hypercalls are passed with KVM_EXIT_HYPERCALL in +kvm_run::hypercall. diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 3ca732feb9a5..25554ce97045 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -123,6 +123,7 @@ struct kvm_arch { * supported. */ bool return_nisv_io_abort_to_user; + bool hvc_to_user; /* * VM-wide PMU filter, implemented as a bitmap and big enough for diff --git a/include/kvm/arm_psci.h b/include/kvm/arm_psci.h index 5b58bd2fe088..d6b71a48fbb1 100644 --- a/include/kvm/arm_psci.h +++ b/include/kvm/arm_psci.h @@ -16,6 +16,10 @@ #define KVM_ARM_PSCI_LATEST KVM_ARM_PSCI_1_0 +#define KVM_PSCI_FN_LAST KVM_PSCI_FN(3) +#define PSCI_0_2_FN_LAST PSCI_0_2_FN(0x3f) +#define PSCI_0_2_FN64_LAST PSCI_0_2_FN64(0x3f) + /* * We need the KVM pointer independently from the vcpu as we can call * this from HYP, and need to apply kern_hyp_va on it... diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 06ba64c49737..aa831986a399 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1084,6 +1084,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_VM_COPY_ENC_CONTEXT_FROM 197 #define KVM_CAP_PTP_KVM 198 #define KVM_CAP_ARM_MP_HALTED 199 +#define KVM_CAP_ARM_HVC_TO_USER 200 #ifdef KVM_CAP_IRQ_ROUTING diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index d6ad977fea5f..074197721e97 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -93,6 +93,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, r = 0; kvm->arch.return_nisv_io_abort_to_user = true; break; + case KVM_CAP_ARM_HVC_TO_USER: + r = 0; + kvm->arch.hvc_to_user = true; + break; default: r = -EINVAL; break; @@ -208,6 +212,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_VCPU_ATTRIBUTES: case KVM_CAP_PTP_KVM: case KVM_CAP_ARM_MP_HALTED: + case KVM_CAP_ARM_HVC_TO_USER: r = 1; break; case KVM_CAP_SET_GUEST_DEBUG2: diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index 30da78f72b3b..ccc2015eddf9 100644 --- a/arch/arm64/kvm/hypercalls.c +++ b/arch/arm64/kvm/hypercalls.c @@ -58,6 +58,28 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val) val[3] = lower_32_bits(cycles); } +static int kvm_hvc_user(struct kvm_vcpu *vcpu) +{ + int i; + struct kvm_run *run = vcpu->run; + + if (!vcpu->kvm->arch.hvc_to_user) { + smccc_set_retval(vcpu, SMCCC_RET_NOT_SUPPORTED, 0, 0, 0); + return 1; + } + + run->exit_reason = KVM_EXIT_HYPERCALL; + run->hypercall.nr = kvm_vcpu_hvc_get_imm(vcpu); + /* Copy the first parameters for fast access */ + for (i = 0; i < 6; i++) + run->hypercall.args[i] = vcpu_get_reg(vcpu, i); + run->hypercall.ret = 0; + run->hypercall.longmode = 0; + run->hypercall.pad = 0; + + return 0; +} + int kvm_hvc_call_handler(struct kvm_vcpu *vcpu) { u32 func_id = smccc_get_function(vcpu); @@ -139,8 +161,12 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu) case ARM_SMCCC_TRNG_RND32: case ARM_SMCCC_TRNG_RND64: return kvm_trng_call(vcpu); - default: + case KVM_PSCI_FN_BASE...KVM_PSCI_FN_LAST: + case PSCI_0_2_FN_BASE...PSCI_0_2_FN_LAST: + case PSCI_0_2_FN64_BASE...PSCI_0_2_FN64_LAST: return kvm_psci_call(vcpu); + default: + return kvm_hvc_user(vcpu); } smccc_set_retval(vcpu, val[0], val[1], val[2], val[3]);