On Tue, 8 Jun 2021 17:48:05 +0200 Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> wrote: > 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 <james.morse@xxxxxxx> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> Trivial question inline. > --- > > 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@xxxxxxx/ > [2] https://lore.kernel.org/linux-arm-kernel/bf7e83f1-c58e-8d65-edd0-d08f27b8b766@xxxxxxx/ > [3] https://lore.kernel.org/linux-arm-kernel/f56cf420-affc-35f0-2355-801a924b8a35@xxxxxxx/ > --- > 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) Why 3f? Perhaps a spec reference if appropriate. > + > /* > * 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]); _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
