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

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Date: Mon, 6 May 2024 10:41:02 +0800
From: maobibo <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
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



On 2024/5/6 上午9:54, Huacai Chen wrote:
> 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.
yes, uapi kvm_param.h is needed for Loongarch, and there will be problem 
if it is removed. And it should kept unchanged.

Regards
Bibo Mao
> 
> 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
>>
>>