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Message-ID: <CAAhV-H7jY8p8eY4rVLcMvVky9ZQTyZkA+0UsW2JkbKYtWvjmZg@mail.gmail.com>
Date: Tue, 2 Jul 2024 15:28:23 +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 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.
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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