[RFC PATCH 0/3] RISC-V: KVM: Guest Debug Support

[Anup Patel]

On Fri, Dec 22, 2023 at 1:59 PM Chao Du <duchao at eswincomputing.com> wrote:
>
> On 2023-12-21 21:01, Anup Patel <apatel at ventanamicro.com> wrote:
> >
> > On Thu, Dec 21, 2023 at 3:21 PM Chao Du <duchao at eswincomputing.com> wrote:
> > >
> > > This series implements KVM Guest Debug on RISC-V. Currently, we can
> > > debug RISC-V KVM guest from the host side, with software breakpoints.
> > >
> > > A brief test was done on QEMU RISC-V hypervisor emulator.
> > >
> > > A TODO list which will be added later:
> > > 1. HW breakpoints support
> > > 2. Test cases
> >
> > Himanshu has already done the complete HW breakpoint implementation
> > in OpenSBI, Linux RISC-V, and KVM RISC-V. This is based on the upcoming
> > SBI debug trigger extension draft proposal.
> > (Refer, https://lists.riscv.org/g/tech-debug/message/1261)
> >
> > There are also RISE projects to track these efforts:
> > https://wiki.riseproject.dev/pages/viewpage.action?pageId=394541
> > https://wiki.riseproject.dev/pages/viewpage.action?pageId=394545
> >
> > Currently, we are in the process of upstreaming the OpenSBI support
> > for SBI debug trigger extension. The Linux RISC-V and KVM RISC-V
> > patches require SBI debug trigger extension and Sdtrig extension to
> > be frozen which will happen next year 2024.
> >
> > Regards,
> > Anup
> >
>
> Hi Anup,
>
> Thank you for the information and your great work on the SBI
> Debug Trigger Extension proposal.
>
> So I think that 'HW breakpoints support' in the above TODO list
> will be taken care of by Himanshu following the extension proposal.
>
> On the other hand, if I understand correctly, the software
> breakpoint part of KVM Guest Debug has no dependency on the new
> extension since it does not use the trigger module. Just an
> ebreak substitution is made.
>
> So may I know your suggestion about this RFC? Both in KVM and QEMU.

Sorry for the delay in response due to holiday season other
stuff keeping me busy.

If this is about ebreak instruction virtualization then this series
needs following changes:
1) Update cover letter to indicate this series focus on ebreak
     instruction virtualization
2) PATCH1 and PATCH2 can be merged into one PATCH1
3) Include a new patch which adds KVM selftest for ebreak
    based guest debug. This selftest will test both:
    A) Taking "ebreak" trap from guest as KVM_EXIT_DEBUG
         in host user-space
    B) Taking "ebreak" trap from guest as BREAKPOINT
        exception in guest

Regards,
Anup

>
> Regards,
> Chao
>
> > >
> > > This series is based on Linux 6.7-rc6 and is also available at:
> > > https://github.com/Du-Chao/linux/tree/riscv_gd_sw
> > >
> > > The matched QEMU is available at:
> > > https://github.com/Du-Chao/qemu/tree/riscv_gd_sw
> > >
> > > Chao Du (3):
> > >   RISC-V: KVM: Enable the KVM_CAP_SET_GUEST_DEBUG capability
> > >   RISC-V: KVM: Implement kvm_arch_vcpu_ioctl_set_guest_debug()
> > >   RISC-V: KVM: Handle breakpoint exits for VCPU
> > >
> > >  arch/riscv/include/uapi/asm/kvm.h |  1 +
> > >  arch/riscv/kvm/vcpu.c             | 15 +++++++++++++--
> > >  arch/riscv/kvm/vcpu_exit.c        |  4 ++++
> > >  arch/riscv/kvm/vm.c               |  1 +
> > >  4 files changed, 19 insertions(+), 2 deletions(-)
> > >
> > > --
> > > 2.17.1
> > >
> > >
> > > --
> > > kvm-riscv mailing list
> > > kvm-riscv at lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/kvm-riscv