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Message-ID: <521ca7c6-64a2-53fa-5cff-b366ae73f600@loongson.cn>
Date: Mon, 30 Dec 2024 10:12:10 +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
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.
How about adding function kvm_complete_hypercall() like
kvm_complete_mmio_read(), such as:
--- 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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