RE: [PATCH v5 3/4] iommufd: Add IOMMU_GET_HW_INFO

[Liu, Yi L]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Friday, August 4, 2023 10:12 PM
> 
> 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@xxxxxxxxxx>
> > > Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > > ---
> > >   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 {}

How about below?

diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 94c498b8fdf6..a8bb7da87036 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 +178,80 @@ 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) {
+		data = ops->hw_info(idev->dev, &data_len, &hw_info_type);
+		if (IS_ERR(data)) {
+			rc = PTR_ERR(data);
+			goto err_put;
+		}
+
+		/* 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 err_free;
+		}
+
+		length = min(cmd->data_len, data_len);
+		if (copy_to_user(user_ptr, data, length)) {
+			rc = -EFAULT;
+			goto err_free;
+		}
+	}
+
+	/*
+	 * 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 err_free;
+	}
+
+	cmd->data_len = length;
+	cmd->out_data_type = hw_info_type;
+	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
+
+err_free:
+	kfree(data);
+err_put:
+	iommufd_put_object(&idev->obj);
+	return rc;
+}
+
 static int iommufd_fops_open(struct inode *inode, struct file *filp)
 {
 	struct iommufd_ctx *ictx;

Regards,
Yi Liu

> > > +	/*
> > > +	 * 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