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SubjectRe: [RFC PATCH v2 04/19] RISC-V: Add initial skeletal KVM support
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On 02/08/19 09:47, Anup Patel wrote:
> +static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
> +{
> + if (kvm_request_pending(vcpu)) {
> + /* TODO: */
> +
> + /*
> + * Clear IRQ_PENDING requests that were made to guarantee
> + * that a VCPU sees new virtual interrupts.
> + */
> + kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);
> + }
> +}

This kvm_check_request can go away (as it does in patch 6).

> +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +{
> + int ret;
> + unsigned long scause, stval;

You need to wrap this with srcu_read_lock/srcu_read_unlock, otherwise
stage2_page_fault can access freed memslot arrays. (ARM doesn't have
this issue because it does not have to decode instructions on MMIO faults).

That is,

vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);

> + /* Process MMIO value returned from user-space */
> + if (run->exit_reason == KVM_EXIT_MMIO) {
> + ret = kvm_riscv_vcpu_mmio_return(vcpu, vcpu->run);
> + if (ret)
> + return ret;
> + }
> +
> + if (run->immediate_exit)
> + return -EINTR;
> +
> + vcpu_load(vcpu);
> +
> + kvm_sigset_activate(vcpu);
> +
> + ret = 1;
> + run->exit_reason = KVM_EXIT_UNKNOWN;
> + while (ret > 0) {
> + /* Check conditions before entering the guest */
> + cond_resched();
> +
> + kvm_riscv_check_vcpu_requests(vcpu);
> +
> + preempt_disable();
> +
> + local_irq_disable();
> +
> + /*
> + * Exit if we have a signal pending so that we can deliver
> + * the signal to user space.
> + */
> + if (signal_pending(current)) {
> + ret = -EINTR;
> + run->exit_reason = KVM_EXIT_INTR;
> + }

Add an srcu_read_unlock here (and then the smp_store_mb can become
smp_mb__after_srcu_read_unlock + WRITE_ONCE).


> + /*
> + * Ensure we set mode to IN_GUEST_MODE after we disable
> + * interrupts and before the final VCPU requests check.
> + * See the comment in kvm_vcpu_exiting_guest_mode() and
> + * Documentation/virtual/kvm/vcpu-requests.rst
> + */
> + smp_store_mb(vcpu->mode, IN_GUEST_MODE);
> +
> + if (ret <= 0 ||
> + kvm_request_pending(vcpu)) {
> + vcpu->mode = OUTSIDE_GUEST_MODE;
> + local_irq_enable();
> + preempt_enable();
> + continue;
> + }
> +
> + guest_enter_irqoff();
> +
> + __kvm_riscv_switch_to(&vcpu->arch);
> +
> + vcpu->mode = OUTSIDE_GUEST_MODE;
> + vcpu->stat.exits++;
> +
> + /* Save SCAUSE and STVAL because we might get an interrupt
> + * between __kvm_riscv_switch_to() and local_irq_enable()
> + * which can potentially overwrite SCAUSE and STVAL.
> + */
> + scause = csr_read(CSR_SCAUSE);
> + stval = csr_read(CSR_STVAL);
> +
> + /*
> + * We may have taken a host interrupt in VS/VU-mode (i.e.
> + * while executing the guest). This interrupt is still
> + * pending, as we haven't serviced it yet!
> + *
> + * We're now back in HS-mode with interrupts disabled
> + * so enabling the interrupts now will have the effect
> + * of taking the interrupt again, in HS-mode this time.
> + */
> + local_irq_enable();
> +
> + /*
> + * We do local_irq_enable() before calling guest_exit() so
> + * that if a timer interrupt hits while running the guest
> + * we account that tick as being spent in the guest. We
> + * enable preemption after calling guest_exit() so that if
> + * we get preempted we make sure ticks after that is not
> + * counted as guest time.
> + */
> + guest_exit();
> +
> + preempt_enable();

And another srcu_read_lock here. Using vcpu->srcu_idx instead of a
local variable also allows system_opcode_insn to wrap kvm_vcpu_block
with a srcu_read_unlock/srcu_read_lock pair.

> + ret = kvm_riscv_vcpu_exit(vcpu, run, scause, stval);
> + }
> +
> + kvm_sigset_deactivate(vcpu);

And finally srcu_read_unlock here.

Paolo

> + vcpu_put(vcpu);
> + return ret;
> +}
> diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
> new file mode 100644
> index 000000000000..e4d7c8f0807a
> --- /dev/null
> +++ b/arch/riscv/kvm/vcpu_exit.c
> @@ -0,0 +1,35 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Western Digital Corporation or its affiliates.
> + *
> + * Authors:
> + * Anup Patel <anup.patel@wdc.com>
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/err.h>
> +#include <linux/kvm_host.h>
> +
> +/**
> + * kvm_riscv_vcpu_mmio_return -- Handle MMIO loads after user space emulation
> + * or in-kernel IO emulation
> + *
> + * @vcpu: The VCPU pointer
> + * @run: The VCPU run struct containing the mmio data
> + */
> +int kvm_riscv_vcpu_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +{
> + /* TODO: */
> + return 0;
> +}
> +
> +/*
> + * Return > 0 to return to guest, < 0 on error, 0 (and set exit_reason) on
> + * proper exit to userspace.
> + */
> +int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
> + unsigned long scause, unsigned long stval)
> +{
> + /* TODO: */
> + return 0;
> +}
> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> new file mode 100644
> index 000000000000..ac0211820521
> --- /dev/null
> +++ b/arch/riscv/kvm/vm.c
> @@ -0,0 +1,79 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Western Digital Corporation or its affiliates.
> + *
> + * Authors:
> + * Anup Patel <anup.patel@wdc.com>
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/err.h>
> +#include <linux/module.h>
> +#include <linux/uaccess.h>
> +#include <linux/kvm_host.h>
> +
> +int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
> +{
> + /* TODO: To be added later. */
> + return -ENOTSUPP;
> +}
> +
> +int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> +{
> + int r;
> +
> + r = kvm_riscv_stage2_alloc_pgd(kvm);
> + if (r)
> + return r;
> +
> + return 0;
> +}
> +
> +void kvm_arch_destroy_vm(struct kvm *kvm)
> +{
> + int i;
> +
> + for (i = 0; i < KVM_MAX_VCPUS; ++i) {
> + if (kvm->vcpus[i]) {
> + kvm_arch_vcpu_destroy(kvm->vcpus[i]);
> + kvm->vcpus[i] = NULL;
> + }
> + }
> +}
> +
> +int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> +{
> + int r;
> +
> + switch (ext) {
> + case KVM_CAP_DEVICE_CTRL:
> + case KVM_CAP_USER_MEMORY:
> + case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
> + case KVM_CAP_ONE_REG:
> + case KVM_CAP_READONLY_MEM:
> + case KVM_CAP_MP_STATE:
> + case KVM_CAP_IMMEDIATE_EXIT:
> + r = 1;
> + break;
> + case KVM_CAP_NR_VCPUS:
> + r = num_online_cpus();
> + break;
> + case KVM_CAP_MAX_VCPUS:
> + r = KVM_MAX_VCPUS;
> + break;
> + case KVM_CAP_NR_MEMSLOTS:
> + r = KVM_USER_MEM_SLOTS;
> + break;
> + default:
> + r = 0;
> + break;
> + }
> +
> + return r;
> +}
> +
> +long kvm_arch_vm_ioctl(struct file *filp,
> + unsigned int ioctl, unsigned long arg)
> +{
> + return -EINVAL;
> +}
>

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