linux-kernel - Re: [PATCH v4 2/3] LoongArch: KVM: Add LBT feature detection function

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Date: Sun, 30 Jun 2024 10:07:53 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <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

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.

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
>