Re: [PATCH] LoongArch: KVM: Add hypercall service support for usermode VMM

[Huacai Chen]

Hi, Bibo,

Is this patch trying to do the same thing as "LoongArch: add hypcall
to emulate syscall in kvm" in 4.19?

Huacai

On Mon, Dec 23, 2024 at 4:42 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>
> Some VMMs provides special hypercall service in usermode, KVM need
> not handle the usermode hypercall service and pass it to VMM and
> let VMM handle it.
>
> Here new code KVM_HCALL_CODE_USER is added for user-mode hypercall
> service, KVM loads all six registers to VMM.
>
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
>  arch/loongarch/include/asm/kvm_host.h      |  1 +
>  arch/loongarch/include/asm/kvm_para.h      |  2 ++
>  arch/loongarch/include/uapi/asm/kvm_para.h |  1 +
>  arch/loongarch/kvm/exit.c                  | 22 ++++++++++++++++++++++
>  arch/loongarch/kvm/vcpu.c                  |  3 +++
>  5 files changed, 29 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
> index 7b8367c39da8..590982cd986e 100644
> --- a/arch/loongarch/include/asm/kvm_host.h
> +++ b/arch/loongarch/include/asm/kvm_host.h
> @@ -162,6 +162,7 @@ enum emulation_result {
>  #define LOONGARCH_PV_FEAT_UPDATED      BIT_ULL(63)
>  #define LOONGARCH_PV_FEAT_MASK         (BIT(KVM_FEATURE_IPI) |         \
>                                          BIT(KVM_FEATURE_STEAL_TIME) |  \
> +                                        BIT(KVM_FEATURE_USER_HCALL) |  \
>                                          BIT(KVM_FEATURE_VIRT_EXTIOI))
>
>  struct kvm_vcpu_arch {
> diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
> index c4e84227280d..d3c00de484f6 100644
> --- a/arch/loongarch/include/asm/kvm_para.h
> +++ b/arch/loongarch/include/asm/kvm_para.h
> @@ -13,12 +13,14 @@
>
>  #define KVM_HCALL_CODE_SERVICE         0
>  #define KVM_HCALL_CODE_SWDBG           1
> +#define KVM_HCALL_CODE_USER            2
>
>  #define KVM_HCALL_SERVICE              HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_SERVICE)
>  #define  KVM_HCALL_FUNC_IPI            1
>  #define  KVM_HCALL_FUNC_NOTIFY         2
>
>  #define KVM_HCALL_SWDBG                        HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_SWDBG)
> +#define KVM_HCALL_USER_SERVICE         HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_USER)
>
>  /*
>   * LoongArch hypercall return code
> diff --git a/arch/loongarch/include/uapi/asm/kvm_para.h b/arch/loongarch/include/uapi/asm/kvm_para.h
> index b0604aa9b4bb..76d802ef01ce 100644
> --- a/arch/loongarch/include/uapi/asm/kvm_para.h
> +++ b/arch/loongarch/include/uapi/asm/kvm_para.h
> @@ -17,5 +17,6 @@
>  #define  KVM_FEATURE_STEAL_TIME                2
>  /* BIT 24 - 31 are features configurable by user space vmm */
>  #define  KVM_FEATURE_VIRT_EXTIOI       24
> +#define  KVM_FEATURE_USER_HCALL                25
>
>  #endif /* _UAPI_ASM_KVM_PARA_H */
> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
> index a7893bd01e73..1a85cd4fb6a5 100644
> --- a/arch/loongarch/kvm/exit.c
> +++ b/arch/loongarch/kvm/exit.c
> @@ -873,6 +873,28 @@ static int kvm_handle_hypercall(struct kvm_vcpu *vcpu)
>                 vcpu->stat.hypercall_exits++;
>                 kvm_handle_service(vcpu);
>                 break;
> +       case KVM_HCALL_USER_SERVICE:
> +               if (!kvm_guest_has_pv_feature(vcpu, KVM_FEATURE_USER_HCALL)) {
> +                       kvm_write_reg(vcpu, LOONGARCH_GPR_A0, KVM_HCALL_INVALID_CODE);
> +                       break;
> +               }
> +
> +               vcpu->run->exit_reason = KVM_EXIT_HYPERCALL;
> +               vcpu->run->hypercall.nr = KVM_HCALL_USER_SERVICE;
> +               vcpu->run->hypercall.args[0] = kvm_read_reg(vcpu, LOONGARCH_GPR_A0);
> +               vcpu->run->hypercall.args[1] = kvm_read_reg(vcpu, LOONGARCH_GPR_A1);
> +               vcpu->run->hypercall.args[2] = kvm_read_reg(vcpu, LOONGARCH_GPR_A2);
> +               vcpu->run->hypercall.args[3] = kvm_read_reg(vcpu, LOONGARCH_GPR_A3);
> +               vcpu->run->hypercall.args[4] = kvm_read_reg(vcpu, LOONGARCH_GPR_A4);
> +               vcpu->run->hypercall.args[5] = kvm_read_reg(vcpu, LOONGARCH_GPR_A5);
> +               vcpu->run->hypercall.flags = 0;
> +               /*
> +                * Set invalid return value by default
> +                * Need user-mode VMM modify it
> +                */
> +               vcpu->run->hypercall.ret = KVM_HCALL_INVALID_CODE;
> +               ret = RESUME_HOST;
> +               break;
>         case KVM_HCALL_SWDBG:
>                 /* KVM_HCALL_SWDBG only in effective when SW_BP is enabled */
>                 if (vcpu->guest_debug & KVM_GUESTDBG_SW_BP_MASK) {
> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index d18a4a270415..8c46ad1872ee 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -1735,6 +1735,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>         if (run->exit_reason == KVM_EXIT_LOONGARCH_IOCSR) {
>                 if (!run->iocsr_io.is_write)
>                         kvm_complete_iocsr_read(vcpu, run);
> +       } else if (run->exit_reason == KVM_EXIT_HYPERCALL) {
> +               kvm_write_reg(vcpu, LOONGARCH_GPR_A0, run->hypercall.ret);
> +               update_pc(&vcpu->arch);
>         }
>
>         if (!vcpu->wants_to_run)
>
> base-commit: 48f506ad0b683d3e7e794efa60c5785c4fdc86fa
> --
> 2.39.3
>