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

["Chao Du" <duchao@eswincomputing.com>]

On 2024-02-14 21:19, Anup Patel <apatel@ventanamicro.com> wrote:
> 
> On Tue, Feb 6, 2024 at 1:22 PM Chao Du <duchao@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@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
> 

Thanks for the review and detailed suggestion.
Maybe we could make it a bit easier:
1) The kvm_arch_vcpu_ioctl_set_guest_debug() only update vcpu->guest_debug
   accordingly.
2) The kvm_riscv_vcpu_swap_in_guest_state() check vcpu->guest_debug and
   set/clear the HEDELEG csr accordingly.

Could you confirm if this is OK?
If yes, I will post another revision.

Regards,
Chao

> > +
> > +       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
> >
> >
> > --
> > kvm-riscv mailing list
> > kvm-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kvm-riscv