linux-kernel - Re: [RFC v3 2/8] vfio/type1: Make per-application (VM) PASID quota tunable

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Date:   Wed, 29 Jan 2020 16:56:32 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     eric.auger@...hat.com, kevin.tian@...el.com,
        jacob.jun.pan@...ux.intel.com, joro@...tes.org,
        ashok.raj@...el.com, jun.j.tian@...el.com, yi.y.sun@...el.com,
        jean-philippe.brucker@....com, peterx@...hat.com,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v3 2/8] vfio/type1: Make per-application (VM) PASID quota
 tunable

On Wed, 29 Jan 2020 04:11:46 -0800
"Liu, Yi L" <yi.l.liu@...el.com> wrote:

> From: Liu Yi L <yi.l.liu@...el.com>
> 
> The PASID quota is per-application (VM) according to vfio's PASID
> management rule. For better flexibility, quota shall be user tunable
> . This patch provides a VFIO based user interface for which quota can
> be adjusted. However, quota cannot be adjusted downward below the
> number of outstanding PASIDs.
> 
> This patch only makes the per-VM PASID quota tunable. While for the
> way to tune the default PASID quota, it may require a new vfio module
> option or other way. This may be another patchset in future.

If we give an unprivileged user the ability to increase their quota,
why do we even have a quota at all?  I figured we were going to have a
module option tunable so its under the control of the system admin.
Thanks,

Alex

> 
> Previous discussions:
> https://patchwork.kernel.org/patch/11209429/
> 
> Cc: Kevin Tian <kevin.tian@...el.com>
> CC: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Cc: Alex Williamson <alex.williamson@...hat.com>
> Cc: Eric Auger <eric.auger@...hat.com>
> Cc: Jean-Philippe Brucker <jean-philippe.brucker@....com>
> Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 33 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/vfio.h       | 22 ++++++++++++++++++++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index e836d04..1cf75f5 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2243,6 +2243,27 @@ static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
>  	return ret;
>  }
>  
> +static int vfio_iommu_type1_set_pasid_quota(struct vfio_iommu *iommu,
> +					    u32 quota)
> +{
> +	struct vfio_mm *vmm = iommu->vmm;
> +	int ret = 0;
> +
> +	mutex_lock(&iommu->lock);
> +	mutex_lock(&vmm->pasid_lock);
> +	if (vmm->pasid_count > quota) {
> +		ret = -EINVAL;
> +		goto out_unlock;
> +	}
> +	vmm->pasid_quota = quota;
> +	ret = quota;
> +
> +out_unlock:
> +	mutex_unlock(&vmm->pasid_lock);
> +	mutex_unlock(&iommu->lock);
> +	return ret;
> +}
> +
>  static long vfio_iommu_type1_ioctl(void *iommu_data,
>  				   unsigned int cmd, unsigned long arg)
>  {
> @@ -2389,6 +2410,18 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  		default:
>  			return -EINVAL;
>  		}
> +	} else if (cmd == VFIO_IOMMU_SET_PASID_QUOTA) {
> +		struct vfio_iommu_type1_pasid_quota quota;
> +
> +		minsz = offsetofend(struct vfio_iommu_type1_pasid_quota,
> +				    quota);
> +
> +		if (copy_from_user(&quota, (void __user *)arg, minsz))
> +			return -EFAULT;
> +
> +		if (quota.argsz < minsz)
> +			return -EINVAL;
> +		return vfio_iommu_type1_set_pasid_quota(iommu, quota.quota);
>  	}
>  
>  	return -ENOTTY;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 298ac80..d4bf415 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -835,6 +835,28 @@ struct vfio_iommu_type1_pasid_request {
>   */
>  #define VFIO_IOMMU_PASID_REQUEST	_IO(VFIO_TYPE, VFIO_BASE + 22)
>  
> +/**
> + * @quota: the new pasid quota which a userspace application (e.g. VM)
> + * is configured.
> + */
> +struct vfio_iommu_type1_pasid_quota {
> +	__u32	argsz;
> +	__u32	flags;
> +	__u32	quota;
> +};
> +
> +/**
> + * VFIO_IOMMU_SET_PASID_QUOTA - _IOW(VFIO_TYPE, VFIO_BASE + 23,
> + *				struct vfio_iommu_type1_pasid_quota)
> + *
> + * Availability of this feature depends on PASID support in the device,
> + * its bus, the underlying IOMMU and the CPU architecture. In VFIO, it
> + * is available after VFIO_SET_IOMMU.
> + *
> + * returns: latest quota on success, -errno on failure.
> + */
> +#define VFIO_IOMMU_SET_PASID_QUOTA	_IO(VFIO_TYPE, VFIO_BASE + 23)
> +
>  /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
>  
>  /*