linux-kernel - Re: [PATCH v4 2/6] LoongArch: KVM: Add hypercall instruction emulation support

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Date: Mon, 19 Feb 2024 12:01:14 +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>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
 kvm@...r.kernel.org
Subject: Re: [PATCH v4 2/6] LoongArch: KVM: Add hypercall instruction
 emulation support


On 2024/2/19 上午10:41, Huacai Chen wrote:
> Hi, Bibo,
> 
> On Thu, Feb 1, 2024 at 11:19 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>
>> On LoongArch system, hypercall instruction is supported when system
>> runs on VM mode. This patch adds dummy function with hypercall
>> instruction emulation, rather than inject EXCCODE_INE invalid
>> instruction exception.
>>
>> 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 93783fa24f6e..22991a6f0e2b 100644
>> --- a/arch/loongarch/include/asm/Kbuild
>> +++ b/arch/loongarch/include/asm/Kbuild
>> @@ -23,4 +23,3 @@ 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..9425d3b7e486
>> --- /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 hypcall return code
> Maybe using "hypercall" in comments is better.
will modify in next patch.

> 
>> + */
>> +#define KVM_HC_STATUS_SUCCESS          0
>> +#define KVM_HC_INVALID_CODE            -1UL
>> +#define KVM_HC_INVALID_PARAMETER       -2UL
> Maybe KVM_HCALL_SUCCESS/KVM_HCALL_INVALID_CODE/KVM_HCALL_PARAMETER is better.
yes, KVM_HCALL_xxxx sounds better. Will modify it.

Regards
Bibo Mao
> 
> Huacai
> 
>> +
>> +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
>> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
>> index ed1d89d53e2e..d15c71320a11 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_hypcall(struct kvm_vcpu *vcpu)
>> +{
>> +       update_pc(&vcpu->arch);
>> +
>> +       /* Treat it as noop intruction, only set return value */
>> +       vcpu->arch.gprs[LOONGARCH_GPR_A0] = KVM_HC_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_hypcall,
>>   };
>>
>>   int kvm_handle_fault(struct kvm_vcpu *vcpu, int fault)
>> --
>> 2.39.3
>>