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Date: Thu, 9 Jan 2020 11:16:36 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: zhenyuw@...ux.intel.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, pbonzini@...hat.com,
kevin.tian@...el.com
Subject: Re: [PATCH 1/2] vfio: introduce vfio_iova_rw to read/write a range
of IOVAs
On Thu, 2 Jan 2020 20:02:17 -0500
Yan Zhao <yan.y.zhao@...el.com> wrote:
> vfio_iova_rw will read/write a range of userspace memory (starting form
> device iova to iova + len -1) into a kenrel buffer without pinning the
> userspace memory.
>
> TODO: vfio needs to mark the iova dirty if vfio_iova_rw(write) is
> called.
>
> Cc: Kevin Tian <kevin.tian@...el.com>
> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> ---
> drivers/vfio/vfio.c | 45 ++++++++++++++++++
> drivers/vfio/vfio_iommu_type1.c | 81 +++++++++++++++++++++++++++++++++
> include/linux/vfio.h | 5 ++
> 3 files changed, 131 insertions(+)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index c8482624ca34..36e91e647ed5 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1961,6 +1961,51 @@ int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn, int npage)
> }
> EXPORT_SYMBOL(vfio_unpin_pages);
>
> +/*
> + * Read/Write a range of userspace IOVAs for a device into/from a kernel
> + * buffer without pinning the userspace memory
> + * @dev [in] : device
> + * @iova [in] : base IOVA of a userspace buffer
> + * @data [in] : pointer to kernel buffer
> + * @len [in] : kernel buffer length
> + * @write : indicate read or write
> + * Return error on failure or 0 on success.
> + */
> +int vfio_iova_rw(struct device *dev, unsigned long iova, void *data,
> + unsigned long len, bool write)
Shouldn't iova be a dma_addr_t and len be a size_t? AIUI this function
performs the equivalent behavior of the device itself performing a DMA.
Hmm, should the interface be named vfio_dma_rw()?
> +{
> + struct vfio_container *container;
> + struct vfio_group *group;
> + struct vfio_iommu_driver *driver;
> + int ret = 0;
> +
> + if (!dev || !data || len <= 0)
> + return -EINVAL;
> +
> + group = vfio_group_get_from_dev(dev);
> + if (!group)
> + return -ENODEV;
> +
> + ret = vfio_group_add_container_user(group);
> + if (ret)
> + goto out;
> +
> + container = group->container;
> + driver = container->iommu_driver;
> +
> + if (likely(driver && driver->ops->iova_rw))
> + ret = driver->ops->iova_rw(container->iommu_data,
> + iova, data, len, write);
> + else
> + ret = -ENOTTY;
> +
> + vfio_group_try_dissolve_container(group);
> +out:
> + vfio_group_put(group);
> + return ret;
> +}
> +EXPORT_SYMBOL(vfio_iova_rw);
> +
> static int vfio_register_iommu_notifier(struct vfio_group *group,
> unsigned long *events,
> struct notifier_block *nb)
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 2ada8e6cdb88..aee191077235 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -27,6 +27,7 @@
> #include <linux/iommu.h>
> #include <linux/module.h>
> #include <linux/mm.h>
> +#include <linux/mmu_context.h>
> #include <linux/rbtree.h>
> #include <linux/sched/signal.h>
> #include <linux/sched/mm.h>
> @@ -2326,6 +2327,85 @@ static int vfio_iommu_type1_unregister_notifier(void *iommu_data,
> return blocking_notifier_chain_unregister(&iommu->notifier, nb);
> }
>
> +static int next_segment(unsigned long len, int offset)
> +{
> + if (len > PAGE_SIZE - offset)
> + return PAGE_SIZE - offset;
> + else
> + return len;
> +}
> +
> +static int vfio_iommu_type1_rw_iova_seg(struct vfio_iommu *iommu,
> + unsigned long iova, void *data,
> + unsigned long seg_len,
> + unsigned long offset,
> + bool write)
> +{
> + struct mm_struct *mm;
> + unsigned long vaddr;
> + struct vfio_dma *dma;
> + bool kthread = current->mm == NULL;
> + int ret = 0;
> +
> + dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
> + if (!dma)
> + return -EINVAL;
> +
> + mm = get_task_mm(dma->task);
> +
> + if (!mm)
> + return -ENODEV;
> +
> + if (kthread)
> + use_mm(mm);
> + else if (current->mm != mm) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + vaddr = dma->vaddr + iova - dma->iova + offset;
Parenthesis here would be useful and might prevent overflow, ie:
dma->vaddr + (iova - dma->iova) + offset
> +
> + ret = write ? __copy_to_user((void __user *)vaddr,
> + data, seg_len) :
> + __copy_from_user(data, (void __user *)vaddr,
> + seg_len);
> + if (ret)
> + ret = -EFAULT;
> +
> + if (kthread)
> + unuse_mm(mm);
> +out:
> + mmput(mm);
> + return ret;
> +}
> +
> +static int vfio_iommu_type1_iova_rw(void *iommu_data, unsigned long iova,
> + void *data, unsigned long len, bool write)
> +{
> + struct vfio_iommu *iommu = iommu_data;
> + int offset = iova & ~PAGE_MASK;
> + int seg_len;
> + int ret = 0;
> +
> + iova = iova & PAGE_MASK;
> +
> + mutex_lock(&iommu->lock);
> + while ((seg_len = next_segment(len, offset)) > 0) {
> + ret = vfio_iommu_type1_rw_iova_seg(iommu, iova, data,
> + seg_len, offset, write);
Why do we need to split operations at page boundaries? It seems really
inefficient that at each page crossing we need to lookup the vfio_dma
again (probably the same one), switch to the mm (probably the same one),
and perform another copy_{to,from}_user() when potentially have
everything we need to perform a larger copy. Thanks,
Alex
> + if (ret)
> + break;
> +
> + offset = 0;
> + len -= seg_len;
> + data += seg_len;
> + iova += PAGE_SIZE;
> + }
> +
> + mutex_unlock(&iommu->lock);
> + return ret;
> +}
> +
> static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
> .name = "vfio-iommu-type1",
> .owner = THIS_MODULE,
> @@ -2338,6 +2418,7 @@ static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
> .unpin_pages = vfio_iommu_type1_unpin_pages,
> .register_notifier = vfio_iommu_type1_register_notifier,
> .unregister_notifier = vfio_iommu_type1_unregister_notifier,
> + .iova_rw = vfio_iommu_type1_iova_rw,
> };
>
> static int __init vfio_iommu_type1_init(void)
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index e42a711a2800..7bf18a31bbcf 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -82,6 +82,8 @@ struct vfio_iommu_driver_ops {
> struct notifier_block *nb);
> int (*unregister_notifier)(void *iommu_data,
> struct notifier_block *nb);
> + int (*iova_rw)(void *iommu_data, unsigned long iova,
> + void *data, unsigned long len, bool write);
> };
>
> extern int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops);
> @@ -107,6 +109,9 @@ extern int vfio_pin_pages(struct device *dev, unsigned long *user_pfn,
> extern int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn,
> int npage);
>
> +extern int vfio_iova_rw(struct device *dev, unsigned long iova, void *data,
> + unsigned long len, bool write);
> +
> /* each type has independent events */
> enum vfio_notify_type {
> VFIO_IOMMU_NOTIFY = 0,
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