When capability KVM_CAP_ARM_HVC_TO_USER is available, userspace can request to handle all hypercalls that aren't handled by KVM. With the help of another capability, this will allow userspace to handle PSCI calls.
Suggested-by: James Morse james.morse@arm.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org ---
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 read them back 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.
* 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 vcpu 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.
* Enabling this using a vCPU arch feature rather than the whole-VM capability would be fine, but it would be difficult to do the same for the following psci-in-user capability. So let's enable everything at the VM scope.
* No idea whether this work out of the box for AArch32 guests.
[1] https://lore.kernel.org/linux-arm-kernel/20170808164616.25949-12-james.morse... [2] https://lore.kernel.org/linux-arm-kernel/bf7e83f1-c58e-8d65-edd0-d08f27b8b76... [3] https://lore.kernel.org/linux-arm-kernel/f56cf420-affc-35f0-2355-801a924b8a3... --- 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 8da6a9940086..1afab8deadb3 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 9934a57db40c..1d8b6dd5d68f 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1083,6 +1083,7 @@ 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 10e1f7832e7f..3c2fcf878b72 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..b00ffd59d10e 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); + /* Add 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]);