[PATCH v1 1/3] RISC-V: KVM: Implement kvm_arch_vcpu_ioctl_set_guest_debug()

[Anup Patel]

On Tue, Feb 6, 2024 at 1:22 PM Chao Du <duchao at eswincomputing.com> wrote:
>
> kvm_vm_ioctl_check_extension(): Return 1 if KVM_CAP_SET_GUEST_DEBUG is
> being checked.
>
> kvm_arch_vcpu_ioctl_set_guest_debug(): Update the guest_debug flags
> from userspace accordingly. Route the breakpoint exceptions to HS mode
> if the VM is being debugged by userspace, by clearing the corresponding
> bit in hedeleg CSR.
>
> Signed-off-by: Chao Du <duchao at eswincomputing.com>
> ---
>  arch/riscv/include/uapi/asm/kvm.h |  1 +
>  arch/riscv/kvm/vcpu.c             | 15 +++++++++++++--
>  arch/riscv/kvm/vm.c               |  1 +
>  3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index d6b7a5b95874..8890977836f0 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -17,6 +17,7 @@
>
>  #define __KVM_HAVE_IRQ_LINE
>  #define __KVM_HAVE_READONLY_MEM
> +#define __KVM_HAVE_GUEST_DEBUG
>
>  #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
>
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index b5ca9f2e98ac..6cee974592ac 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -475,8 +475,19 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
>  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>                                         struct kvm_guest_debug *dbg)
>  {
> -       /* TODO; To be implemented later. */
> -       return -EINVAL;
> +       if (dbg->control & KVM_GUESTDBG_ENABLE) {
> +               if (vcpu->guest_debug != dbg->control) {
> +                       vcpu->guest_debug = dbg->control;
> +                       csr_clear(CSR_HEDELEG, BIT(EXC_BREAKPOINT));
> +               }
> +       } else {
> +               if (vcpu->guest_debug != 0) {
> +                       vcpu->guest_debug = 0;
> +                       csr_set(CSR_HEDELEG, BIT(EXC_BREAKPOINT));
> +               }
> +       }

This is broken because directly setting breakpoint exception delegation
in CSR also affects other VCPUs running on the same host CPU.

To address the above, we should do the following:
1) Add "unsigned long hedeleg" in "struct kvm_vcpu_config" which
   is pre-initialized in kvm_riscv_vcpu_setup_config() without setting
   EXC_BREAKPOINT bit.
2) The kvm_arch_vcpu_ioctl_set_guest_debug() should only set/clear
    EXC_BREAKPOINT bit in "hedeleg" of "struct kvm_vcpu_config".
3) The kvm_riscv_vcpu_swap_in_guest_state() must write the
     HEDELEG csr before entering the Guest/VM.

Regards,
Anup

> +
> +       return 0;
>  }
>
>  static void kvm_riscv_vcpu_setup_config(struct kvm_vcpu *vcpu)
> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> index ce58bc48e5b8..7396b8654f45 100644
> --- a/arch/riscv/kvm/vm.c
> +++ b/arch/riscv/kvm/vm.c
> @@ -186,6 +186,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>         case KVM_CAP_READONLY_MEM:
>         case KVM_CAP_MP_STATE:
>         case KVM_CAP_IMMEDIATE_EXIT:
> +       case KVM_CAP_SET_GUEST_DEBUG:
>                 r = 1;
>                 break;
>         case KVM_CAP_NR_VCPUS:
> --
> 2.17.1
>
>
> --
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