linux-kernel - Re: [PATCH v5 3/4] iommufd: Add IOMMU_GET_HW

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Date:   Fri, 4 Aug 2023 11:12:11 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, kevin.tian@...el.com,
        robin.murphy@....com, cohuck@...hat.com, eric.auger@...hat.com,
        nicolinc@...dia.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        zhenzhong.duan@...el.com
Subject: Re: [PATCH v5 3/4] iommufd: Add IOMMU_GET_HW_INFO

On Fri, Aug 04, 2023 at 09:59:11AM +0800, Baolu Lu wrote:
> On 2023/8/3 22:31, Yi Liu wrote:
> > Under nested IOMMU translation, userspace owns the stage-1 translation
> > table (e.g. the stage-1 page table of Intel VT-d or the context table
> > of ARM SMMUv3, and etc.). Stage-1 translation tables are vendor specific,
> > and need to be compatiable with the underlying IOMMU hardware. Hence,
> 
>                  compatible
> 
> > userspace should know the IOMMU hardware capability before creating and
> > configuring the stage-1 translation table to kernel.
> > 
> > This adds IOMMU_GET_HW_INFO ioctl to query the IOMMU hardware information
> > (a.k.a capability) for a given device. The returned data is vendor specific,
> > userspace needs to decode it with the structure mapped by the @out_data_type
> > field.
> > 
> > As only physical devices have IOMMU hardware, so this will return error
> > if the given device is not a physical device.
> > 
> > Co-developed-by: Nicolin Chen <nicolinc@...dia.com>
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > Signed-off-by: Yi Liu <yi.l.liu@...el.com>
> > ---
> >   drivers/iommu/iommufd/main.c | 79 ++++++++++++++++++++++++++++++++++++
> >   include/uapi/linux/iommufd.h | 36 ++++++++++++++++
> >   2 files changed, 115 insertions(+)
> > 
> > diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
> > index 94c498b8fdf6..a0302bcaa97c 100644
> > --- a/drivers/iommu/iommufd/main.c
> > +++ b/drivers/iommu/iommufd/main.c
> > @@ -17,6 +17,7 @@
> >   #include <linux/bug.h>
> >   #include <uapi/linux/iommufd.h>
> >   #include <linux/iommufd.h>
> > +#include "../iommu-priv.h"
> >   #include "io_pagetable.h"
> >   #include "iommufd_private.h"
> > @@ -177,6 +178,81 @@ static int iommufd_destroy(struct iommufd_ucmd *ucmd)
> >   	return 0;
> >   }
> > +static int iommufd_zero_fill_user(void __user *ptr, size_t bytes)
> > +{
> > +	int index = 0;
> > +
> > +	for (; index < bytes; index++) {
> > +		if (put_user(0, (uint8_t __user *)(ptr + index)))
> > +			return -EFAULT;
> > +	}
> > +	return 0;
> > +}
> > +
> > +static int iommufd_get_hw_info(struct iommufd_ucmd *ucmd)
> > +{
> > +	u32 hw_info_type = IOMMU_HW_INFO_TYPE_NONE;
> > +	struct iommu_hw_info *cmd = ucmd->cmd;
> > +	unsigned int length = 0, data_len;
> > +	struct iommufd_device *idev;
> > +	const struct iommu_ops *ops;
> > +	void __user *user_ptr;
> > +	void *data = NULL;
> > +	int rc = 0;
> > +
> > +	if (cmd->flags || cmd->__reserved || !cmd->data_len)
> > +		return -EOPNOTSUPP;
> > +
> > +	idev = iommufd_get_device(ucmd, cmd->dev_id);
> > +	if (IS_ERR(idev))
> > +		return PTR_ERR(idev);
> > +
> > +	user_ptr = u64_to_user_ptr(cmd->data_ptr);
> > +
> > +	ops = dev_iommu_ops(idev->dev);
> > +	if (!ops->hw_info)
> > +		goto done;
> > +
> > +	data = ops->hw_info(idev->dev, &data_len, &hw_info_type);
> > +	if (IS_ERR(data)) {
> > +		rc = PTR_ERR(data);
> > +		goto out_err;
> 
> Can kfree() handle a ERR_PTR input? I am afraid not,
> 
> /**
>  * kfree - free previously allocated memory
>  * @object: pointer returned by kmalloc() or kmem_cache_alloc()
>  *
>  * If @object is NULL, no operation is performed.
>  */
> void kfree(const void *object)
> {
>         struct folio *folio;
>         struct slab *slab;
>         struct kmem_cache *s;
> 
>         trace_kfree(_RET_IP_, object);
> 
>         if (unlikely(ZERO_OR_NULL_PTR(object)))
>                 return;
> 
> So, perhaps we should add
> 
> 	data = NULL;
> 
> before
> 	goto out_err;

No, use more labels.

> > +	}
> > +
> > +	/* driver has hw_info callback should have a unique hw_info_type */
> > +	if (WARN_ON_ONCE(hw_info_type == IOMMU_HW_INFO_TYPE_NONE)) {
> > +		rc = -ENODEV;
> > +		goto out_err;
> > +	}
> > +
> > +	length = min(cmd->data_len, data_len);
> > +	if (copy_to_user(user_ptr, data, length)) {
> > +		rc = -EFAULT;
> > +		goto out_err;
> > +	}
> > +
> > +done:

No label here, put it in a if {}

> > +	/*
> > +	 * Zero the trailing bytes if the user buffer is bigger than the
> > +	 * data size kernel actually has.
> > +	 */
> > +	if (length < cmd->data_len) {
> > +		rc = iommufd_zero_fill_user(user_ptr + length,
> > +					    cmd->data_len - length);
> > +		if (rc)
> > +			goto out_err;
> > +	}
> > +
> > +	cmd->data_len = length;
> > +	cmd->out_data_type = hw_info_type;
> > +	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
> > +
> > +out_err:

err_free:
> > +	kfree(data);

err_put:

> > +	iommufd_put_object(&idev->obj);
> > +	return rc;
> > +}

Jason