On Thu, 30 Mar 2023 16:49:13 +0100, Oliver Upton <oliver.upton@xxxxxxxxx> wrote: > > In anticipation of user hypercall filters, add the necessary plumbing to > get SMCCC calls out to userspace. Even though the exit structure has > space for KVM to pass register arguments, let's just avoid it altogether > and let userspace poke at the registers via KVM_GET_ONE_REG. > > This deliberately stretches the definition of a 'hypercall' to cover > SMCs from EL1 in addition to the HVCs we know and love. KVM doesn't > support EL1 calls into secure services, but now we can paint that as a > userspace problem and be done with it. > > Finally, we need a flag to let userspace know what conduit instruction > was used (i.e. SMC vs. HVC). > > Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx> > --- > Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++-- > arch/arm64/include/uapi/asm/kvm.h | 4 ++++ > arch/arm64/kvm/handle_exit.c | 4 +++- > arch/arm64/kvm/hypercalls.c | 17 +++++++++++++++++ > 4 files changed, 44 insertions(+), 3 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 9b01e3d0e757..c8ab2f730945 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -6221,11 +6221,29 @@ to the byte array. > __u64 flags; > } 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). > + > +It is strongly recommended that userspace use ``KVM_EXIT_IO`` (x86) or > +``KVM_EXIT_MMIO`` (all except s390) to implement functionality that > +requires a guest to interact with host userpace. > > .. note:: KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO. > > +For arm64: > +---------- > + > +SMCCC exits can be enabled depending on the configuration of the SMCCC > +filter. See the Documentation/virt/kvm/devices/vm.rst > +``KVM_ARM_SMCCC_FILTER`` for more details. Maybe this hunk should come with the following patch which actually adds that doc. > + > +``nr`` contains the function ID of the guest's SMCCC call. Userspace is > +expected to use the ``KVM_GET_ONE_REG`` ioctl to retrieve the call > +parameters from the vCPU's GPRs. > + > +Definition of ``flags``: > + - ``KVM_HYPERCALL_EXIT_SMC``: Indicates that the guest used the SMC > + conduit to initiate the SMCCC call. If this bit is 0 then the guest > + used the HVC conduit for the SMCCC call. > + > :: > > /* KVM_EXIT_TPR_ACCESS */ > diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h > index bbab92402510..1dabb7d05514 100644 > --- a/arch/arm64/include/uapi/asm/kvm.h > +++ b/arch/arm64/include/uapi/asm/kvm.h > @@ -472,12 +472,16 @@ enum { > enum kvm_smccc_filter_action { > KVM_SMCCC_FILTER_ALLOW = 0, > KVM_SMCCC_FILTER_DENY, > + KVM_SMCCC_FILTER_FWD_TO_USER, > > #ifdef __KERNEL__ > NR_SMCCC_FILTER_ACTIONS > #endif > }; > > +/* arm64-specific KVM_EXIT_HYPERCALL flags */ > +#define KVM_HYPERCALL_EXIT_SMC (1U << 0) > + > #endif > > #endif /* __ARM_KVM_H__ */ > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index 68f95dcd41a1..3f43e20c48b6 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -71,7 +71,9 @@ static int handle_smc(struct kvm_vcpu *vcpu) > * Trap exception, not a Secure Monitor Call exception [...]" > * > * We need to advance the PC after the trap, as it would > - * otherwise return to the same address... > + * otherwise return to the same address. Furthermore, pre-incrementing > + * the PC before potentially exiting to userspace maintains the same > + * abstraction for both SMCs and HVCs. > */ > kvm_incr_pc(vcpu); > > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c > index 73b218ddd1a5..7e8c850847c1 100644 > --- a/arch/arm64/kvm/hypercalls.c > +++ b/arch/arm64/kvm/hypercalls.c > @@ -180,6 +180,19 @@ static u8 kvm_smccc_get_action(struct kvm_vcpu *vcpu, u32 func_id) > return KVM_SMCCC_FILTER_DENY; > } > > +static void kvm_prepare_hypercall_exit(struct kvm_vcpu *vcpu, u32 func_id) > +{ > + u8 ec = ESR_ELx_EC(kvm_vcpu_get_esr(vcpu)); > + struct kvm_run *run = vcpu->run; > + > + run->exit_reason = KVM_EXIT_HYPERCALL; > + run->hypercall.nr = func_id; > + run->hypercall.flags = 0; > + > + if (ec == ESR_ELx_EC_SMC32 || ec == ESR_ELx_EC_SMC64) > + run->hypercall.flags |= KVM_HYPERCALL_EXIT_SMC; > +} > + > int kvm_smccc_call_handler(struct kvm_vcpu *vcpu) > { > struct kvm_smccc_features *smccc_feat = &vcpu->kvm->arch.smccc_feat; > @@ -192,6 +205,10 @@ int kvm_smccc_call_handler(struct kvm_vcpu *vcpu) > action = kvm_smccc_get_action(vcpu, func_id); > if (action == KVM_SMCCC_FILTER_DENY) > goto out; > + if (action == KVM_SMCCC_FILTER_FWD_TO_USER) { > + kvm_prepare_hypercall_exit(vcpu, func_id); > + return 0; > + } nit: maybe write this as a switch statement? > > switch (func_id) { > case ARM_SMCCC_VERSION_FUNC_ID: Thanks, M. -- Without deviation from the norm, progress is not possible.