Add a suspend request and move the WFI execution into check_vcpu_requests(), next to the power-off logic. This will allow userspace implementing PSCI to request WFI before returning to the guest.

Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org

--- There is a compatibility question regarding the GET_MP_STATE ioctl. Since older userspace does not know about the new KVM_MP_STATE_HALTED, we cannot return that, otherwise we'll break their mp_state support. Not a risk at the moment because we don't return to userspace with HALTED state (WFI and PSCI both stay in the run loop until the suspend request is consumed). But I'm not 100% sure of that and it will certainly change in the future. I'd rather explicitly return RUNNABLE in GET_MP_STATE, but I kept it simple for the moment - we'll probably toss the patch anyway. --- arch/arm64/include/asm/kvm_host.h | 2 ++ arch/arm64/kvm/arm.c | 18 ++++++++++++++- arch/arm64/kvm/handle_exit.c | 3 +-- arch/arm64/kvm/psci.c | 37 +++++++++++++------------------ 4 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 55a04f4d5919..3ca732feb9a5 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -46,6 +46,7 @@ #define KVM_REQ_VCPU_RESET KVM_ARCH_REQ(2) #define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3) #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4) +#define KVM_REQ_SUSPEND KVM_ARCH_REQ(5)

#define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \ KVM_DIRTY_LOG_INITIALLY_SET) @@ -722,6 +723,7 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr); void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu); bool kvm_arm_vcpu_is_off(struct kvm_vcpu *vcpu); +void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu);

/* Guest/host FPSIMD coordination helpers */ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu); diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index e4a8bf1b638b..4a42d54299db 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -447,6 +447,12 @@ bool kvm_arm_vcpu_is_off(struct kvm_vcpu *vcpu) return vcpu->arch.mp_state == KVM_MP_STATE_STOPPED; }

+void kvm_arm_vcpu_suspend(struct kvm_vcpu *vcpu) +{ + vcpu->arch.mp_state = KVM_MP_STATE_HALTED; + kvm_make_request(KVM_REQ_SUSPEND, vcpu); +} + int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu, struct kvm_mp_state *mp_state) { @@ -667,6 +673,8 @@ static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)

static void check_vcpu_requests(struct kvm_vcpu *vcpu) { + bool irq_pending; + if (kvm_request_pending(vcpu)) { if (kvm_check_request(KVM_REQ_SLEEP, vcpu)) vcpu_req_sleep(vcpu); @@ -678,7 +686,7 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu) * Clear IRQ_PENDING requests that were made to guarantee * that a VCPU sees new virtual interrupts. */ - kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu); + irq_pending = kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);

if (kvm_check_request(KVM_REQ_RECORD_STEAL, vcpu)) kvm_update_stolen_time(vcpu); @@ -690,6 +698,14 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu) vgic_v4_load(vcpu); preempt_enable(); } + + if (kvm_check_request(KVM_REQ_SUSPEND, vcpu)) { + if (!irq_pending) { + kvm_vcpu_block(vcpu); + kvm_clear_request(KVM_REQ_UNHALT, vcpu); + } + vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE; + } } }

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index 6f48336b1d86..9717df3104cf 100644 --- a/arch/arm64/kvm/handle_exit.c +++ b/arch/arm64/kvm/handle_exit.c @@ -95,8 +95,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu) } else { trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false); vcpu->stat.wfi_exit_stat++; - kvm_vcpu_block(vcpu); - kvm_clear_request(KVM_REQ_UNHALT, vcpu); + kvm_arm_vcpu_suspend(vcpu); }

kvm_incr_pc(vcpu); diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c index 24b4a2265dbd..42a307ceb95f 100644 --- a/arch/arm64/kvm/psci.c +++ b/arch/arm64/kvm/psci.c @@ -31,27 +31,6 @@ static unsigned long psci_affinity_mask(unsigned long affinity_level) return 0; }

-static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu) -{ - /* - * NOTE: For simplicity, we make VCPU suspend emulation to be - * same-as WFI (Wait-for-interrupt) emulation. - * - * This means for KVM the wakeup events are interrupts and - * this is consistent with intended use of StateID as described - * in section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A). - * - * Further, we also treat power-down request to be same as - * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2 - * specification (ARM DEN 0022A). This means all suspend states - * for KVM will preserve the register state. - */ - kvm_vcpu_block(vcpu); - kvm_clear_request(KVM_REQ_UNHALT, vcpu); - - return PSCI_RET_SUCCESS; -} - static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu) { struct vcpu_reset_state *reset_state; @@ -227,7 +206,21 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu) break; case PSCI_0_2_FN_CPU_SUSPEND: case PSCI_0_2_FN64_CPU_SUSPEND: - val = kvm_psci_vcpu_suspend(vcpu); + /* + * NOTE: For simplicity, we make VCPU suspend emulation to be + * same-as WFI (Wait-for-interrupt) emulation. + * + * This means for KVM the wakeup events are interrupts and this + * is consistent with intended use of StateID as described in + * section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A). + * + * Further, we also treat power-down request to be same as + * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2 + * specification (ARM DEN 0022A). This means all suspend states + * for KVM will preserve the register state. + */ + kvm_arm_vcpu_suspend(vcpu); + val = PSCI_RET_SUCCESS; break; case PSCI_0_2_FN_CPU_OFF: kvm_arm_vcpu_power_off(vcpu);

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]);

The CPU_SUSPEND function is mandatory in PSCI v0.2+. As KVM handles timer interrupts and IPIs with the vGIC, it can implement wait-for- interrupt more easily than userspace. To implement CPU_SUSPEND, tell KVM to wait for interrupts before returning to the guest.

Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- target/arm/cpu.h | 3 +++ target/arm/kvm.c | 17 +++++++++++++---- target/arm/psci.c | 14 +++++++++----- 3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h index 02ab8495665..fdc09e27b1a 100644 --- a/target/arm/cpu.h +++ b/target/arm/cpu.h @@ -882,6 +882,9 @@ struct ARMCPU { /* KVM steal time */ OnOffAuto kvm_steal_time;

+ /* Put the vCPU in WFI before returning to the guest */ + bool kvm_suspend; + /* Uniprocessor system with MP extensions */ bool mp_is_up;

diff --git a/target/arm/kvm.c b/target/arm/kvm.c index 56e460b388f..1a7e52b6bad 100644 --- a/target/arm/kvm.c +++ b/target/arm/kvm.c @@ -38,6 +38,7 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = { };

static bool cap_has_mp_state; +static bool cap_has_mp_halted; static bool cap_has_inject_serror_esr; static bool cap_has_inject_ext_dabt;

@@ -256,6 +257,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) kvm_halt_in_kernel_allowed = true;

cap_has_mp_state = kvm_check_extension(s, KVM_CAP_MP_STATE); + cap_has_mp_halted = kvm_check_extension(s, KVM_CAP_ARM_MP_HALTED);

if (ms->smp.cpus > 256 && !kvm_check_extension(s, KVM_CAP_ARM_IRQ_LINE_LAYOUT_2)) { @@ -672,10 +674,16 @@ void kvm_arm_create_host_vcpu(ARMCPU *cpu) int kvm_arm_sync_mpstate_to_kvm(ARMCPU *cpu) { if (cap_has_mp_state) { - struct kvm_mp_state mp_state = { - .mp_state = (cpu->power_state == PSCI_OFF) ? - KVM_MP_STATE_STOPPED : KVM_MP_STATE_RUNNABLE - }; + struct kvm_mp_state mp_state = {}; + + if (cpu->power_state == PSCI_OFF) { + mp_state.mp_state = KVM_MP_STATE_STOPPED; + } else if (cap_has_mp_halted && cpu->kvm_suspend) { + mp_state.mp_state = KVM_MP_STATE_HALTED; + } else { + mp_state.mp_state = KVM_MP_STATE_RUNNABLE; + } + int ret = kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MP_STATE, &mp_state); if (ret) { fprintf(stderr, "%s: failed to set MP_STATE %d/%s\n", @@ -702,6 +710,7 @@ int kvm_arm_sync_mpstate_to_qemu(ARMCPU *cpu) } cpu->power_state = (mp_state.mp_state == KVM_MP_STATE_STOPPED) ? PSCI_OFF : PSCI_ON; + cpu->kvm_suspend = (mp_state.mp_state == KVM_MP_STATE_HALTED); }

return 0; diff --git a/target/arm/psci.c b/target/arm/psci.c index 6709e280133..3a980c7f2bf 100644 --- a/target/arm/psci.c +++ b/target/arm/psci.c @@ -21,6 +21,7 @@ #include "exec/helper-proto.h" #include "kvm-consts.h" #include "qemu/main-loop.h" +#include "sysemu/kvm.h" #include "sysemu/runstate.h" #include "internals.h" #include "arm-powerctl.h" @@ -184,13 +185,16 @@ void arm_handle_psci_call(ARMCPU *cpu) ret = QEMU_PSCI_RET_INVALID_PARAMS; break; } - /* Powerdown is not supported, we always go into WFI */ - if (is_a64(env)) { - env->xregs[0] = 0; + /* + * Powerdown is not supported, we always go into WFI. + * Under KVM, let the kernel suspend the vCPU. + */ + if (kvm_enabled()) { + cpu->kvm_suspend = true; } else { - env->regs[0] = 0; + helper_wfi(env, 4); } - helper_wfi(env, 4); + ret = QEMU_ARM_POWERCTL_RET_SUCCESS; break; case QEMU_PSCI_0_1_FN_MIGRATE: case QEMU_PSCI_0_2_FN_MIGRATE:

For CPU_ON, check whether a CPU is disabled or if it actually does not exit. Return NOT_PRESENT rather than INVALID_PARAMS in the former case.

This requires an update to the PSCI spec. As of PSCI v1.1, NOT_PRESENT isn't a valid return value for CPU_ON.

Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- target/arm/arm-powerctl.h | 1 + target/arm/arm-powerctl.c | 44 +++++++++++++++++++++++++++++++-------- 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/target/arm/arm-powerctl.h b/target/arm/arm-powerctl.h index 37c8a04f0a9..258f8570e8e 100644 --- a/target/arm/arm-powerctl.h +++ b/target/arm/arm-powerctl.h @@ -18,6 +18,7 @@ #define QEMU_ARM_POWERCTL_ALREADY_ON QEMU_PSCI_RET_ALREADY_ON #define QEMU_ARM_POWERCTL_IS_OFF QEMU_PSCI_RET_DENIED #define QEMU_ARM_POWERCTL_ON_PENDING QEMU_PSCI_RET_ON_PENDING +#define QEMU_ARM_POWERCTL_NOT_PRESENT QEMU_PSCI_RET_NOT_PRESENT

/* * arm_get_cpu_by_id: diff --git a/target/arm/arm-powerctl.c b/target/arm/arm-powerctl.c index b75f813b403..d80eec70b6a 100644 --- a/target/arm/arm-powerctl.c +++ b/target/arm/arm-powerctl.c @@ -13,6 +13,7 @@ #include "cpu-qom.h" #include "internals.h" #include "arm-powerctl.h" +#include "hw/boards.h" #include "qemu/log.h" #include "qemu/main-loop.h"

@@ -27,18 +28,37 @@ } \ } while (0)

+static CPUArchId *arm_get_archid_by_id(uint64_t id) +{ + int n; + CPUArchId *arch_id; + MachineState *ms = MACHINE(qdev_get_machine()); + + /* + * At this point disabled CPUs don't have a CPUState, but their CPUArchId + * exists. + * + * TODO: Is arch_id == mp_affinity? This needs work. + */ + for (n = 0; n < ms->possible_cpus->len; n++) { + arch_id = &ms->possible_cpus->cpus[n]; + + if (arch_id->arch_id == id) { + return arch_id; + } + } + return NULL; +} + CPUState *arm_get_cpu_by_id(uint64_t id) { - CPUState *cpu; + CPUArchId *arch_id;

DPRINTF("cpu %" PRId64 "\n", id);

- CPU_FOREACH(cpu) { - ARMCPU *armcpu = ARM_CPU(cpu); - - if (armcpu->mp_affinity == id) { - return cpu; - } + arch_id = arm_get_archid_by_id(id); + if (arch_id && arch_id->cpu) { + return CPU(arch_id->cpu); }

qemu_log_mask(LOG_GUEST_ERROR, @@ -145,6 +165,7 @@ int arm_set_cpu_on(uint64_t cpuid, uint64_t entry, uint64_t context_id, { CPUState *target_cpu_state; ARMCPU *target_cpu; + CPUArchId *arch_id; struct CpuOnInfo *info;

assert(qemu_mutex_iothread_locked()); @@ -165,11 +186,16 @@ int arm_set_cpu_on(uint64_t cpuid, uint64_t entry, uint64_t context_id, }

/* Retrieve the cpu we are powering up */ - target_cpu_state = arm_get_cpu_by_id(cpuid); - if (!target_cpu_state) { + arch_id = arm_get_archid_by_id(cpuid); + if (!arch_id) { /* The cpu was not found */ return QEMU_ARM_POWERCTL_INVALID_PARAM; } + if (!arch_id->cpu) { + /* The cpu is not plugged in */ + return QEMU_ARM_POWERCTL_NOT_PRESENT; + } + target_cpu_state = CPU(arch_id->cpu);

target_cpu = ARM_CPU(target_cpu_state); if (target_cpu->power_state == PSCI_ON) {

From: James Morse [mailto:james.morse@arm.com] Sent: Thursday, June 3, 2021 4:39 PM To: Jean-Philippe Brucker jean-philippe@linaro.org; linaro-open-discussions@op-lists.linaro.org Cc: Salil Mehta salil.mehta@huawei.com; Jonathan Cameron jonathan.cameron@huawei.com; lorenzo.pieralisi@arm.com Subject: Re: [RFC linux 0/5] KVM: arm64: Let userspace handle PSCI

'lo

On 20/05/2021 14:07, Jean-Philippe Brucker wrote:

...

As planned during the vCPU hot-add discussions from previous LOD meetings, this prototype lets userspace handle PSCI calls from a guest.

The vCPU hot-add model preferred by Arm presents all possible resources through ACPI at boot time, only marking unavailable vCPUs as hidden. The VMM prevents bringing up those vCPUs by rejecting PSCI CPU_ON calls. This allows to keep things simple for vCPU scaling enablement, while leaving the door open for hardware CPU hot-add.

This series focuses on moving PSCI support into userspace. Patches 1-3 allow userspace to request WFI to be executed by KVM. That way the VMM can easily implement the CPU_SUSPEND function, which is mandatory from PSCI v0.2 onwards (even if it doesn't have a more useful implementation than WFI, natively available to the guest). An alternative would be to poll the vGIC implemented in KVM for interrupts, but I haven't explored that solution. Patches 4 and 5 let the VMM request PSCI calls.

As mentioned on the call, I've tested the udev output on x86 and arm64, as expected its the same: | root@vm:~# udevadm monitor | monitor will print the received events for: | UDEV - the event which udev sends out after rule processing | KERNEL - the kernel uevent | | KERNEL[33.935817] add /devices/system/cpu/cpu1 (cpu) | KERNEL[33.946333] bind /devices/system/cpu/cpu1 (cpu) | UDEV [33.953251] add /devices/system/cpu/cpu1 (cpu) | UDEV [33.958676] bind /devices/system/cpu/cpu1 (cpu)

(I've not played with the KVM changes yet)

...

The guest needs additional support to deal with hidden CPUs and to gracefully handle the "NOT_PRESENT" return value from PSCI CPU_ON. The full prototype can be found here:

Hopefully its possible to make those silent!

Regarding PSCI, I believe you are referring to the return value in the below code hunk(s) and the PSCI spec changes mentioned in the patch[1]?

@@ -209,6 +209,8 @@ static int __psci_cpu_on(u32 fn, unsigned long cpuid, unsigned long entry_point) int err;

err = invoke_psci_fn(fn, cpuid, entry_point, 0); + if (err == PSCI_RET_NOT_PRESENT) + return -EPROBE_DEFER; return psci_to_linux_errno(err); }

[1] https://jpbrucker.net/git/linux/commit/?h=cpuhp/devel&id=afa4089cb122637...

Perhaps, by "additional" support with the hidden cpus you mean its effect on the sizing of various data-structures and other features dependent on the explicit awareness of the present and possible cpus?

Salil.