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Message-ID: <8f0aae2f-f8ba-818b-8faf-08b24d448080@loongson.cn>
Date: Mon, 23 Dec 2024 17:36:26 +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 2024/12/23 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?
yes, it is not only for private vmm, it can be used for qemu also if
there is requirement in future.
> 2, Why 4.19 doesn't need something like "vcpu->run->hypercall.args[0]
> = kvm_read_reg(vcpu, LOONGARCH_GPR_A0);"
The private vmm and private kernel uses stack to pass to parameter,
which are private interface.
For KVM hypercall specification, at most six registers can be used for
input parameter and one register A0 used for output parameter.
> 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.
yes, will do in this way.
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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