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Message-ID: <CAAhV-H520i-2N0DUPO=RJxtU8Sn+eofQAy7_e+rRsnNdgv8DTQ@mail.gmail.com>
Date: Tue, 2 Jul 2024 23:43:56 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: maobibo <maobibo@...ngson.cn>
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 v4 2/3] LoongArch: KVM: Add LBT feature detection function
On Tue, Jul 2, 2024 at 4:42 PM maobibo <maobibo@...ngson.cn> wrote:
>
>
>
> On 2024/7/2 下午3:28, Huacai Chen wrote:
> > On Tue, Jul 2, 2024 at 12:13 PM maobibo <maobibo@...ngson.cn> wrote:
> >>
> >>
> >>
> >> On 2024/7/2 上午10:34, Huacai Chen wrote:
> >>> On Tue, Jul 2, 2024 at 10:25 AM maobibo <maobibo@...ngson.cn> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 2024/7/2 上午9:59, Huacai Chen wrote:
> >>>>> On Tue, Jul 2, 2024 at 9:51 AM maobibo <maobibo@...ngson.cn> wrote:
> >>>>>>
> >>>>>> Huacai,
> >>>>>>
> >>>>>> On 2024/7/1 下午6:26, Huacai Chen wrote:
> >>>>>>> On Mon, Jul 1, 2024 at 9:27 AM maobibo <maobibo@...ngson.cn> wrote:
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Huacai,
> >>>>>>>>
> >>>>>>>> On 2024/6/30 上午10:07, Huacai Chen wrote:
> >>>>>>>>> Hi, Bibo,
> >>>>>>>>>
> >>>>>>>>> On Wed, Jun 26, 2024 at 2:32 PM Bibo Mao <maobibo@...ngson.cn> wrote:
> >>>>>>>>>>
> >>>>>>>>>> Two kinds of LBT feature detection are added here, one is VCPU
> >>>>>>>>>> feature, the other is VM feature. VCPU feature dection can only
> >>>>>>>>>> work with VCPU thread itself, and requires VCPU thread is created
> >>>>>>>>>> already. So LBT feature detection for VM is added also, it can
> >>>>>>>>>> be done even if VM is not created, and also can be done by any
> >>>>>>>>>> thread besides VCPU threads.
> >>>>>>>>>>
> >>>>>>>>>> Loongson Binary Translation (LBT) feature is defined in register
> >>>>>>>>>> cpucfg2. Here LBT capability detection for VCPU is added.
> >>>>>>>>>>
> >>>>>>>>>> Here ioctl command KVM_HAS_DEVICE_ATTR is added for VM, and macro
> >>>>>>>>>> KVM_LOONGARCH_VM_FEAT_CTRL is added to check supported feature. And
> >>>>>>>>>> three sub-features relative with LBT are added as following:
> >>>>>>>>>> KVM_LOONGARCH_VM_FEAT_X86BT
> >>>>>>>>>> KVM_LOONGARCH_VM_FEAT_ARMBT
> >>>>>>>>>> KVM_LOONGARCH_VM_FEAT_MIPSBT
> >>>>>>>>>>
> >>>>>>>>>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> >>>>>>>>>> ---
> >>>>>>>>>> arch/loongarch/include/uapi/asm/kvm.h | 6 ++++
> >>>>>>>>>> arch/loongarch/kvm/vcpu.c | 6 ++++
> >>>>>>>>>> arch/loongarch/kvm/vm.c | 44 ++++++++++++++++++++++++++-
> >>>>>>>>>> 3 files changed, 55 insertions(+), 1 deletion(-)
> >>>>>>>>>>
> >>>>>>>>>> diff --git a/arch/loongarch/include/uapi/asm/kvm.h b/arch/loongarch/include/uapi/asm/kvm.h
> >>>>>>>>>> index ddc5cab0ffd0..c40f7d9ffe13 100644
> >>>>>>>>>> --- a/arch/loongarch/include/uapi/asm/kvm.h
> >>>>>>>>>> +++ b/arch/loongarch/include/uapi/asm/kvm.h
> >>>>>>>>>> @@ -82,6 +82,12 @@ struct kvm_fpu {
> >>>>>>>>>> #define KVM_IOC_CSRID(REG) LOONGARCH_REG_64(KVM_REG_LOONGARCH_CSR, REG)
> >>>>>>>>>> #define KVM_IOC_CPUCFG(REG) LOONGARCH_REG_64(KVM_REG_LOONGARCH_CPUCFG, REG)
> >>>>>>>>>>
> >>>>>>>>>> +/* Device Control API on vm fd */
> >>>>>>>>>> +#define KVM_LOONGARCH_VM_FEAT_CTRL 0
> >>>>>>>>>> +#define KVM_LOONGARCH_VM_FEAT_X86BT 0
> >>>>>>>>>> +#define KVM_LOONGARCH_VM_FEAT_ARMBT 1
> >>>>>>>>>> +#define KVM_LOONGARCH_VM_FEAT_MIPSBT 2
> >>>>>>>>>> +
> >>>>>>>>>> /* Device Control API on vcpu fd */
> >>>>>>>>>> #define KVM_LOONGARCH_VCPU_CPUCFG 0
> >>>>>>>>>> #define KVM_LOONGARCH_VCPU_PVTIME_CTRL 1
> >>>>>>>>> If you insist that LBT should be a vm feature, then I suggest the
> >>>>>>>>> above two also be vm features. Though this is an UAPI change, but
> >>>>>>>>> CPUCFG is upstream in 6.10-rc1 and 6.10-final hasn't been released. We
> >>>>>>>>> have a chance to change it now.
> >>>>>>>>
> >>>>>>>> KVM_LOONGARCH_VCPU_PVTIME_CTRL need be attr percpu since every vcpu
> >>>>>>>> has is own different gpa address.
> >>>>>>> Then leave this as a vm feature.
> >>>>>>>
> >>>>>>>>
> >>>>>>>> For KVM_LOONGARCH_VCPU_CPUCFG attr, it will not changed. We cannot break
> >>>>>>>> the API even if it is 6.10-rc1, VMM has already used this. Else there is
> >>>>>>>> uapi breaking now, still will be in future if we cannot control this.
> >>>>>>> UAPI changing before the first release is allowed, which means, we can
> >>>>>>> change this before the 6.10-final, but cannot change it after
> >>>>>>> 6.10-final.
> >>>>>> Now QEMU has already synced uapi to its own directory, also I never hear
> >>>>>> about this, with my experience with uapi change, there is only newly
> >>>>>> added or removed deprecated years ago.
> >>>>>>
> >>>>>> Is there any documentation about UAPI change rules?
> >>>>> No document, but learn from my more than 10 years upstream experience.
> >>>> Can you show me an example about with your rich upstream experience?
> >>> A simple example,
> >>> e877d705704d7c8fe17b6b5ebdfdb14b84c revert
> >>> 1dccdba084897443d116508a8ed71e0ac8a0 and it changes UAPI.
> >>> 1dccdba084897443d116508a8ed71e0ac8a0 is upstream in 6.9-rc1, and
> >>> e877d705704d7c8fe17b6b5ebdfdb14b84c can revert the behavior before
> >>> 6.9-final, but not after that.
> >>>
> >>> Before the first release, the code status is treated as "unstable", so
> >>> revert, modify is allowed. But after the first release, even if an
> >>> "error" should also be treated as a "bad feature".
> >> Huacai,
> >>
> >> Thanks for showing the example.
> >>
> >> For this issue, Can we adding new uapi and mark the old as deprecated?
> >> so that it can be removed after years.
> > Unnecessary, just remove the old one. Deprecation is for the usage
> > after the first release.
> >
> >>
> >> For me, it is too frequent to revert the old uapi, it is not bug and
> >> only that we have better method now. Also QEMU has synchronized the uapi
> >> to its directory already.
> > QEMU also hasn't been released after synchronizing the uapi, so it is
> > OK to remove the old api now.
> No, I will not do such thing. It is just a joke to revert the uapi.
>
> So just create new world and old world on Loongarch system again?
Again, code status before the first release is *unstable*, that status
is not enough to be a "world".
It's your responsibility to make a good design at the beginning, but
you fail to do that. Fortunately we are before the first release;
unfortunately you don't want to do that.
Huacai
>
> Regards
> Bibo, Mao
>
> >
> > Huacai
> >
> >>
> >> Regards
> >> Bibo, Mao
> >>>
> >>> Huacai
> >>>
> >>>
> >>>>>
> >>>>>>>
> >>>>>>>>
> >>>>>>>> How about adding new extra features capability for VM such as?
> >>>>>>>> +#define KVM_LOONGARCH_VM_FEAT_LSX 3
> >>>>>>>> +#define KVM_LOONGARCH_VM_FEAT_LASX 4
> >>>>>>> They should be similar as LBT, if LBT is vcpu feature, they should
> >>>>>>> also be vcpu features; if LBT is vm feature, they should also be vm
> >>>>>>> features.
> >>>>>> On other architectures, with function kvm_vm_ioctl_check_extension()
> >>>>>> KVM_CAP_XSAVE2/KVM_CAP_PMU_CAPABILITY on x86
> >>>>>> KVM_CAP_ARM_PMU_V3/KVM_CAP_ARM_SVE on arm64
> >>>>>> These features are all cpu features, at the same time they are VM features.
> >>>>>>
> >>>>>> If they are cpu features, how does VMM detect validity of these features
> >>>>>> passing from command line? After all VCPUs are created and send bootup
> >>>>>> command to these VCPUs? That is too late, VMM main thread is easy to
> >>>>>> detect feature validity if they are VM features also.
> >>>>>>
> >>>>>> To be honest, I am not familiar with KVM still, only get further
> >>>>>> understanding after actual problems solving. Welcome to give comments,
> >>>>>> however please read more backgroud if you insist on, else there will be
> >>>>>> endless argument again.
> >>>>> I just say CPUCFG/LSX/LASX and LBT should be in the same class, I
> >>>>> haven't insisted on whether they should be vcpu features or vm
> >>>>> features.
> >>>> It is reasonable if LSX/LASX/LBT should be in the same class, since
> >>>> there is feature options such as lsx=on/off,lasx=on/off,lbt=on/off.
> >>>>
> >>>> What is the usage about CPUCFG capability used for VM feature? It is not
> >>>> a detailed feature, it is only feature-set indicator like cpuid.
> >>>>
> >>>> Regards
> >>>> Bibo Mao
> >>>>>
> >>>>> Huacai
> >>>>>
> >>>>>>
> >>>>>> Regards
> >>>>>> Bibo, Mao
> >>>>>>>
> >>>>>>> Huacai
> >>>>>>>
> >>>>>>>>
> >>>>>>>> Regards
> >>>>>>>> Bibo Mao
> >>>>>>>>>
> >>>>>>>>> Huacai
> >>>>>>>>>
> >>>>>>>>>> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> >>>>>>>>>> index 233d28d0e928..9734b4d8db05 100644
> >>>>>>>>>> --- a/arch/loongarch/kvm/vcpu.c
> >>>>>>>>>> +++ b/arch/loongarch/kvm/vcpu.c
> >>>>>>>>>> @@ -565,6 +565,12 @@ static int _kvm_get_cpucfg_mask(int id, u64 *v)
> >>>>>>>>>> *v |= CPUCFG2_LSX;
> >>>>>>>>>> if (cpu_has_lasx)
> >>>>>>>>>> *v |= CPUCFG2_LASX;
> >>>>>>>>>> + if (cpu_has_lbt_x86)
> >>>>>>>>>> + *v |= CPUCFG2_X86BT;
> >>>>>>>>>> + if (cpu_has_lbt_arm)
> >>>>>>>>>> + *v |= CPUCFG2_ARMBT;
> >>>>>>>>>> + if (cpu_has_lbt_mips)
> >>>>>>>>>> + *v |= CPUCFG2_MIPSBT;
> >>>>>>>>>>
> >>>>>>>>>> return 0;
> >>>>>>>>>> case LOONGARCH_CPUCFG3:
> >>>>>>>>>> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
> >>>>>>>>>> index 6b2e4f66ad26..09e05108c68b 100644
> >>>>>>>>>> --- a/arch/loongarch/kvm/vm.c
> >>>>>>>>>> +++ b/arch/loongarch/kvm/vm.c
> >>>>>>>>>> @@ -99,7 +99,49 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >>>>>>>>>> return r;
> >>>>>>>>>> }
> >>>>>>>>>>
> >>>>>>>>>> +static int kvm_vm_feature_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
> >>>>>>>>>> +{
> >>>>>>>>>> + switch (attr->attr) {
> >>>>>>>>>> + case KVM_LOONGARCH_VM_FEAT_X86BT:
> >>>>>>>>>> + if (cpu_has_lbt_x86)
> >>>>>>>>>> + return 0;
> >>>>>>>>>> + return -ENXIO;
> >>>>>>>>>> + case KVM_LOONGARCH_VM_FEAT_ARMBT:
> >>>>>>>>>> + if (cpu_has_lbt_arm)
> >>>>>>>>>> + return 0;
> >>>>>>>>>> + return -ENXIO;
> >>>>>>>>>> + case KVM_LOONGARCH_VM_FEAT_MIPSBT:
> >>>>>>>>>> + if (cpu_has_lbt_mips)
> >>>>>>>>>> + return 0;
> >>>>>>>>>> + return -ENXIO;
> >>>>>>>>>> + default:
> >>>>>>>>>> + return -ENXIO;
> >>>>>>>>>> + }
> >>>>>>>>>> +}
> >>>>>>>>>> +
> >>>>>>>>>> +static int kvm_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
> >>>>>>>>>> +{
> >>>>>>>>>> + switch (attr->group) {
> >>>>>>>>>> + case KVM_LOONGARCH_VM_FEAT_CTRL:
> >>>>>>>>>> + return kvm_vm_feature_has_attr(kvm, attr);
> >>>>>>>>>> + default:
> >>>>>>>>>> + return -ENXIO;
> >>>>>>>>>> + }
> >>>>>>>>>> +}
> >>>>>>>>>> +
> >>>>>>>>>> int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
> >>>>>>>>>> {
> >>>>>>>>>> - return -ENOIOCTLCMD;
> >>>>>>>>>> + struct kvm *kvm = filp->private_data;
> >>>>>>>>>> + void __user *argp = (void __user *)arg;
> >>>>>>>>>> + struct kvm_device_attr attr;
> >>>>>>>>>> +
> >>>>>>>>>> + switch (ioctl) {
> >>>>>>>>>> + case KVM_HAS_DEVICE_ATTR:
> >>>>>>>>>> + if (copy_from_user(&attr, argp, sizeof(attr)))
> >>>>>>>>>> + return -EFAULT;
> >>>>>>>>>> +
> >>>>>>>>>> + return kvm_vm_has_attr(kvm, &attr);
> >>>>>>>>>> + default:
> >>>>>>>>>> + return -EINVAL;
> >>>>>>>>>> + }
> >>>>>>>>>> }
> >>>>>>>>>> --
> >>>>>>>>>> 2.39.3
> >>>>>>>>>>
> >>>>>>>>
> >>>>>>
> >>>>
> >>
>
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