linux-kernel - Re: [PATCH v8 2/6] LoongArch: KVM: Add hypercall instruction emulation support

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Date: Mon, 6 May 2024 09:54:00 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>, Juergen Gross <jgross@...e.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev, 
	kvm@...r.kernel.org
Subject: Re: [PATCH v8 2/6] LoongArch: KVM: Add hypercall instruction
 emulation support

Hi, Bibo,

On Sun, Apr 28, 2024 at 6:05 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> On LoongArch system, there is hypercall instruction special for
> virtualization. When system executes this instruction on host side,
> there is illegal instruction exception reported, however it will
> trap into host when it is executed in VM mode.
>
> When hypercall is emulated, A0 register is set with value
> KVM_HCALL_INVALID_CODE, rather than inject EXCCODE_INE invalid
> instruction exception. So VM can continue to executing the next code.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>  arch/loongarch/include/asm/Kbuild      |  1 -
>  arch/loongarch/include/asm/kvm_para.h  | 26 ++++++++++++++++++++++++++
>  arch/loongarch/include/uapi/asm/Kbuild |  2 --
>  arch/loongarch/kvm/exit.c              | 10 ++++++++++
>  4 files changed, 36 insertions(+), 3 deletions(-)
>  create mode 100644 arch/loongarch/include/asm/kvm_para.h
>  delete mode 100644 arch/loongarch/include/uapi/asm/Kbuild
>
> diff --git a/arch/loongarch/include/asm/Kbuild b/arch/loongarch/include/asm/Kbuild
> index 2dbec7853ae8..c862672ed953 100644
> --- a/arch/loongarch/include/asm/Kbuild
> +++ b/arch/loongarch/include/asm/Kbuild
> @@ -26,4 +26,3 @@ generic-y += poll.h
>  generic-y += param.h
>  generic-y += posix_types.h
>  generic-y += resource.h
> -generic-y += kvm_para.h
> diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
> new file mode 100644
> index 000000000000..d48f993ae206
> --- /dev/null
> +++ b/arch/loongarch/include/asm/kvm_para.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_LOONGARCH_KVM_PARA_H
> +#define _ASM_LOONGARCH_KVM_PARA_H
> +
> +/*
> + * LoongArch hypercall return code
> + */
> +#define KVM_HCALL_STATUS_SUCCESS       0
> +#define KVM_HCALL_INVALID_CODE         -1UL
> +#define KVM_HCALL_INVALID_PARAMETER    -2UL
> +
> +static inline unsigned int kvm_arch_para_features(void)
> +{
> +       return 0;
> +}
> +
> +static inline unsigned int kvm_arch_para_hints(void)
> +{
> +       return 0;
> +}
> +
> +static inline bool kvm_check_and_clear_guest_paused(void)
> +{
> +       return false;
> +}
> +#endif /* _ASM_LOONGARCH_KVM_PARA_H */
> diff --git a/arch/loongarch/include/uapi/asm/Kbuild b/arch/loongarch/include/uapi/asm/Kbuild
> deleted file mode 100644
> index 4aa680ca2e5f..000000000000
> --- a/arch/loongarch/include/uapi/asm/Kbuild
> +++ /dev/null
> @@ -1,2 +0,0 @@
> -# SPDX-License-Identifier: GPL-2.0
> -generic-y += kvm_para.h
This file shouldn't be removed.

Huacai

> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
> index ed1d89d53e2e..923bbca9bd22 100644
> --- a/arch/loongarch/kvm/exit.c
> +++ b/arch/loongarch/kvm/exit.c
> @@ -685,6 +685,15 @@ static int kvm_handle_lasx_disabled(struct kvm_vcpu *vcpu)
>         return RESUME_GUEST;
>  }
>
> +static int kvm_handle_hypercall(struct kvm_vcpu *vcpu)
> +{
> +       update_pc(&vcpu->arch);
> +
> +       /* Treat it as noop intruction, only set return value */
> +       vcpu->arch.gprs[LOONGARCH_GPR_A0] = KVM_HCALL_INVALID_CODE;
> +       return RESUME_GUEST;
> +}
> +
>  /*
>   * LoongArch KVM callback handling for unimplemented guest exiting
>   */
> @@ -716,6 +725,7 @@ static exit_handle_fn kvm_fault_tables[EXCCODE_INT_START] = {
>         [EXCCODE_LSXDIS]                = kvm_handle_lsx_disabled,
>         [EXCCODE_LASXDIS]               = kvm_handle_lasx_disabled,
>         [EXCCODE_GSPR]                  = kvm_handle_gspr,
> +       [EXCCODE_HVC]                   = kvm_handle_hypercall,
>  };
>
>  int kvm_handle_fault(struct kvm_vcpu *vcpu, int fault)
> --
> 2.39.3
>
>