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>
---
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)
+
/*
* 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]);
--
2.31.1
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