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Message-ID: <8814cf39-0842-ec48-c578-e5e6eeda2295@loongson.cn>
Date: Tue, 31 Dec 2024 17:26:35 +0800
From: bibo mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>, WANG Xuerui <kernel@...0n.name>,
kvm@...r.kernel.org, loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: KVM: Add hypercall service support for
usermode VMM
On 2024/12/31 下午4:41, Huacai Chen wrote:
> On Mon, Dec 30, 2024 at 10:13 AM bibo mao <maobibo@...ngson.cn> wrote:
>>
>> Hi Huacai,
>>
>> On 2024/12/23 下午5:05, Huacai Chen wrote:
>>> I also tried to port an untested version, but I think your version is
>>> a tested one.
>>> https://github.com/chenhuacai/linux/commit/e6596b0e45c80756794aba74ac086c5c0e0306eb
>>>
>>> And I have some questions:
>>> 1, "user service" is not only for syscall, so you rename it?
>>> 2, Why 4.19 doesn't need something like "vcpu->run->hypercall.args[0]
>>> = kvm_read_reg(vcpu, LOONGARCH_GPR_A0);"
>>> 3, I think my version about "vcpu->run->exit_reason =
>>> KVM_EXIT_HYPERCALL;" and "update_pc()" is a little better than yours,
>>> so you can improve them.
>> After a second thought, update_pc() before return to user may be not
>> strictly right, since user VMM can dump registers including pc which is
>> advanced already.
> Agree, and we can see how others do.
>
>>
>> How about adding function kvm_complete_hypercall() like
>> kvm_complete_mmio_read(), such as:
> kvm_complete_user_service() maybe better? Since the "classic
> hypercall" doesn't come here.
sure, will do rename it with kvm_complete_user_service.
>
> And we may also need to set vcpu->run->exit_reason for all cases,
> which is done in my version.
By my understanding, exit_reason need be set only for RESUME_HOST.
it is unnecessary for RESUME_GUEST.
Regards
Bibo Mao
>
> Huacai
>
>> --- a/arch/loongarch/kvm/exit.c
>> +++ b/arch/loongarch/kvm/exit.c
>> +int kvm_complete_hypercall(struct kvm_vcpu *vcpu, struct kvm_run *run)
>> +{
>> + update_pc(&vcpu->arch);
>> + kvm_write_reg(vcpu, LOONGARCH_GPR_A0, run->hypercall.ret);
>> +}
>> +
>> --- a/arch/loongarch/kvm/vcpu.c
>> +++ b/arch/loongarch/kvm/vcpu.c
>> @@ -1736,8 +1736,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>> 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);
>> + kvm_complete_hypercall(vcpu, run);
>> + run->exit_reason = KVM_EXIT_UNKNOWN;
>> }
>>
>> Regards
>> Bibo Mao
>>>
>>> Huacai
>>>
>>> On Mon, Dec 23, 2024 at 4:54 PM bibo mao <maobibo@...ngson.cn> wrote:
>>>>
>>>>
>>>>
>>>> On 2024/12/23 下午4:50, Huacai Chen wrote:
>>>>> Hi, Bibo,
>>>>>
>>>>> Is this patch trying to do the same thing as "LoongArch: add hypcall
>>>>> to emulate syscall in kvm" in 4.19?
>>>> yes, it is to do so -:)
>>>>
>>>> Regards
>>>> Bibo Mao
>>>>>
>>>>> Huacai
>>>>>
>>>>> On Mon, Dec 23, 2024 at 4:42 PM Bibo Mao <maobibo@...ngson.cn> 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@...ngson.cn>
>>>>>> ---
>>>>>> 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
>>>>>>
>>>>
>>>>
>>
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