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References: <20240403140116.3002809-1-vineeth@bitbyteword.org> <20240403140116.3002809-4-vineeth@bitbyteword.org>
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From: Vineeth Remanan Pillai <vineeth@bitbyteword.org>
Date: Mon, 8 Apr 2024 09:59:31 -0400
Message-ID: <CAO7JXPjwEBPqCLcz8ErpgZU5VYdMnz4YORwbuMPM5=qRjOZBBQ@mail.gmail.com>
Subject: Re: [RFC PATCH v2 3/5] kvm: interface for managing pvsched driver for
 guest VMs
To: Ben Segall <bsegall@google.com>, Borislav Petkov <bp@alien8.de>, 
	Daniel Bristot de Oliveira <bristot@redhat.com>, Dave Hansen <dave.hansen@linux.intel.com>, 
	Dietmar Eggemann <dietmar.eggemann@arm.com>, "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, 
	Juri Lelli <juri.lelli@redhat.com>, Mel Gorman <mgorman@suse.de>, 
	Paolo Bonzini <pbonzini@redhat.com>, Andy Lutomirski <luto@kernel.org>, 
	Peter Zijlstra <peterz@infradead.org>, Sean Christopherson <seanjc@google.com>, 
	Thomas Gleixner <tglx@linutronix.de>, Valentin Schneider <vschneid@redhat.com>, 
	Vincent Guittot <vincent.guittot@linaro.org>, Vitaly Kuznetsov <vkuznets@redhat.com>, 
	Wanpeng Li <wanpengli@tencent.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, Joel Fernandes <joel@joelfernandes.org>, 
	Suleiman Souhlal <suleiman@google.com>, Masami Hiramatsu <mhiramat@kernel.org>, himadrics@inria.fr, 
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, 
	Tejun Heo <tj@kernel.org>, Barret Rhoden <brho@google.com>, David Vernet <dvernet@meta.com>, 
	Josh Don <joshdon@google.com>
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Adding sched_ext folks

On Wed, Apr 3, 2024 at 10:01=E2=80=AFAM Vineeth Pillai (Google)
<vineeth@bitbyteword.org> wrote:
>
> Implement ioctl for assigning and unassigning pvsched driver for a
> guest. VMMs would need to adopt this ioctls for supporting the feature.
> Also add a temporary debugfs interface for managing this.
>
> Ideally, the hypervisor would be able to determine the pvsched driver
> based on the information received from the guest. Guest VMs with the
> feature enabled would request hypervisor to select a pvsched driver.
> ioctl api is an override mechanism to give more control to the admin.
>
> Signed-off-by: Vineeth Pillai (Google) <vineeth@bitbyteword.org>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>  include/uapi/linux/kvm.h |   6 ++
>  virt/kvm/kvm_main.c      | 117 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 123 insertions(+)
>
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index c3308536482b..4b29bdad4188 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -2227,4 +2227,10 @@ struct kvm_create_guest_memfd {
>         __u64 reserved[6];
>  };
>
> +struct kvm_pvsched_ops {
> +       __u8 ops_name[32]; /* PVSCHED_NAME_MAX */
> +};
> +
> +#define KVM_GET_PVSCHED_OPS            _IOR(KVMIO, 0xe4, struct kvm_pvsc=
hed_ops)
> +#define KVM_REPLACE_PVSCHED_OPS                _IOWR(KVMIO, 0xe5, struct=
 kvm_pvsched_ops)
>  #endif /* __LINUX_KVM_H */
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 0546814e4db7..b3d9c362d2e3 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1223,6 +1223,79 @@ static void kvm_destroy_vm_debugfs(struct kvm *kvm=
)
>         }
>  }
>
> +#ifdef CONFIG_PARAVIRT_SCHED_KVM
> +static int pvsched_vcpu_ops_show(struct seq_file *m, void *data)
> +{
> +       char ops_name[PVSCHED_NAME_MAX];
> +       struct pvsched_vcpu_ops *ops;
> +       struct kvm *kvm =3D (struct kvm *) m->private;
> +
> +       rcu_read_lock();
> +       ops =3D rcu_dereference(kvm->pvsched_ops);
> +       if (ops)
> +               strncpy(ops_name, ops->name, PVSCHED_NAME_MAX);
> +       rcu_read_unlock();
> +
> +       seq_printf(m, "%s\n", ops_name);
> +
> +       return 0;
> +}
> +
> +static ssize_t
> +pvsched_vcpu_ops_write(struct file *filp, const char __user *ubuf,
> +               size_t cnt, loff_t *ppos)
> +{
> +       int ret;
> +       char *cmp;
> +       char buf[PVSCHED_NAME_MAX];
> +       struct inode *inode;
> +       struct kvm *kvm;
> +
> +       if (cnt > PVSCHED_NAME_MAX)
> +               return -EINVAL;
> +
> +       if (copy_from_user(&buf, ubuf, cnt))
> +               return -EFAULT;
> +
> +       cmp =3D strstrip(buf);
> +
> +       inode =3D file_inode(filp);
> +       inode_lock(inode);
> +       kvm =3D (struct kvm *)inode->i_private;
> +       ret =3D kvm_replace_pvsched_ops(kvm, cmp);
> +       inode_unlock(inode);
> +
> +       if (ret)
> +               return ret;
> +
> +       *ppos +=3D cnt;
> +       return cnt;
> +}
> +
> +static int pvsched_vcpu_ops_open(struct inode *inode, struct file *filp)
> +{
> +       return single_open(filp, pvsched_vcpu_ops_show, inode->i_private)=
;
> +}
> +
> +static const struct file_operations pvsched_vcpu_ops_fops =3D {
> +       .open           =3D pvsched_vcpu_ops_open,
> +       .write          =3D pvsched_vcpu_ops_write,
> +       .read           =3D seq_read,
> +       .llseek         =3D seq_lseek,
> +       .release        =3D single_release,
> +};
> +
> +static void kvm_create_vm_pvsched_debugfs(struct kvm *kvm)
> +{
> +       debugfs_create_file("pvsched_vcpu_ops", 0644, kvm->debugfs_dentry=
, kvm,
> +                           &pvsched_vcpu_ops_fops);
> +}
> +#else
> +static void kvm_create_vm_pvsched_debugfs(struct kvm *kvm)
> +{
> +}
> +#endif
> +
>  static int kvm_create_vm_debugfs(struct kvm *kvm, const char *fdname)
>  {
>         static DEFINE_MUTEX(kvm_debugfs_lock);
> @@ -1288,6 +1361,8 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, c=
onst char *fdname)
>                                     &stat_fops_per_vm);
>         }
>
> +       kvm_create_vm_pvsched_debugfs(kvm);
> +
>         ret =3D kvm_arch_create_vm_debugfs(kvm);
>         if (ret)
>                 goto out_err;
> @@ -5474,6 +5549,48 @@ static long kvm_vm_ioctl(struct file *filp,
>                 r =3D kvm_gmem_create(kvm, &guest_memfd);
>                 break;
>         }
> +#endif
> +#ifdef CONFIG_PARAVIRT_SCHED_KVM
> +       case KVM_REPLACE_PVSCHED_OPS:
> +               struct pvsched_vcpu_ops *ops;
> +               struct kvm_pvsched_ops in_ops, out_ops;
> +
> +               r =3D -EFAULT;
> +               if (copy_from_user(&in_ops, argp, sizeof(in_ops)))
> +                       goto out;
> +
> +               out_ops.ops_name[0] =3D 0;
> +
> +               rcu_read_lock();
> +               ops =3D rcu_dereference(kvm->pvsched_ops);
> +               if (ops)
> +                       strncpy(out_ops.ops_name, ops->name, PVSCHED_NAME=
_MAX);
> +               rcu_read_unlock();
> +
> +               r =3D kvm_replace_pvsched_ops(kvm, (char *)in_ops.ops_nam=
e);
> +               if (r)
> +                       goto out;
> +
> +               r =3D -EFAULT;
> +               if (copy_to_user(argp, &out_ops, sizeof(out_ops)))
> +                       goto out;
> +
> +               r =3D 0;
> +               break;
> +       case KVM_GET_PVSCHED_OPS:
> +               out_ops.ops_name[0] =3D 0;
> +               rcu_read_lock();
> +               ops =3D rcu_dereference(kvm->pvsched_ops);
> +               if (ops)
> +                       strncpy(out_ops.ops_name, ops->name, PVSCHED_NAME=
_MAX);
> +               rcu_read_unlock();
> +
> +               r =3D -EFAULT;
> +               if (copy_to_user(argp, &out_ops, sizeof(out_ops)))
> +                       goto out;
> +
> +               r =3D 0;
> +               break;
>  #endif
>         default:
>                 r =3D kvm_arch_vm_ioctl(filp, ioctl, arg);
> --
> 2.40.1
>