Re: [PATCH v10 7/8] PCI/P2PDMA: Allow userspace VMA allocations through sysfs

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Sep 22, 2022 at 10:39:25AM -0600, Logan Gunthorpe wrote:
> Create a sysfs bin attribute called "allocate" under the existing
> "p2pmem" group. The only allowable operation on this file is the mmap()
> call.
> 
> When mmap() is called on this attribute, the kernel allocates a chunk of
> memory from the genalloc and inserts the pages into the VMA. The
> dev_pagemap .page_free callback will indicate when these pages are no
> longer used and they will be put back into the genalloc.
> 
> On device unbind, remove the sysfs file before the memremap_pages are
> cleaned up. This ensures unmap_mapping_range() is called on the files
> inode and no new mappings can be created.
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>

Not sure which tree this should go through, so:

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/p2pdma.c | 124 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 124 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 4496a7c5c478..a6ed6bbca214 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -89,6 +89,90 @@ static ssize_t published_show(struct device *dev, struct device_attribute *attr,
>  }
>  static DEVICE_ATTR_RO(published);
>  
> +static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
> +		struct bin_attribute *attr, struct vm_area_struct *vma)
> +{
> +	struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
> +	size_t len = vma->vm_end - vma->vm_start;
> +	struct pci_p2pdma *p2pdma;
> +	struct percpu_ref *ref;
> +	unsigned long vaddr;
> +	void *kaddr;
> +	int ret;
> +
> +	/* prevent private mappings from being established */
> +	if ((vma->vm_flags & VM_MAYSHARE) != VM_MAYSHARE) {
> +		pci_info_ratelimited(pdev,
> +				     "%s: fail, attempted private mapping\n",
> +				     current->comm);
> +		return -EINVAL;
> +	}
> +
> +	if (vma->vm_pgoff) {
> +		pci_info_ratelimited(pdev,
> +				     "%s: fail, attempted mapping with non-zero offset\n",
> +				     current->comm);
> +		return -EINVAL;
> +	}
> +
> +	rcu_read_lock();
> +	p2pdma = rcu_dereference(pdev->p2pdma);
> +	if (!p2pdma) {
> +		ret = -ENODEV;
> +		goto out;
> +	}
> +
> +	kaddr = (void *)gen_pool_alloc_owner(p2pdma->pool, len, (void **)&ref);
> +	if (!kaddr) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	/*
> +	 * vm_insert_page() can sleep, so a reference is taken to mapping
> +	 * such that rcu_read_unlock() can be done before inserting the
> +	 * pages
> +	 */
> +	if (unlikely(!percpu_ref_tryget_live_rcu(ref))) {
> +		ret = -ENODEV;
> +		goto out_free_mem;
> +	}
> +	rcu_read_unlock();
> +
> +	for (vaddr = vma->vm_start; vaddr < vma->vm_end; vaddr += PAGE_SIZE) {
> +		ret = vm_insert_page(vma, vaddr, virt_to_page(kaddr));
> +		if (ret) {
> +			gen_pool_free(p2pdma->pool, (uintptr_t)kaddr, len);
> +			return ret;
> +		}
> +		percpu_ref_get(ref);
> +		put_page(virt_to_page(kaddr));
> +		kaddr += PAGE_SIZE;
> +		len -= PAGE_SIZE;
> +	}
> +
> +	percpu_ref_put(ref);
> +
> +	return 0;
> +out_free_mem:
> +	gen_pool_free(p2pdma->pool, (uintptr_t)kaddr, len);
> +out:
> +	rcu_read_unlock();
> +	return ret;
> +}
> +
> +static struct bin_attribute p2pmem_alloc_attr = {
> +	.attr = { .name = "allocate", .mode = 0660 },
> +	.mmap = p2pmem_alloc_mmap,
> +	/*
> +	 * Some places where we want to call mmap (ie. python) will check
> +	 * that the file size is greater than the mmap size before allowing
> +	 * the mmap to continue. To work around this, just set the size
> +	 * to be very large.
> +	 */
> +	.size = SZ_1T,
> +};
> +
>  static struct attribute *p2pmem_attrs[] = {
>  	&dev_attr_size.attr,
>  	&dev_attr_available.attr,
> @@ -96,11 +180,32 @@ static struct attribute *p2pmem_attrs[] = {
>  	NULL,
>  };
>  
> +static struct bin_attribute *p2pmem_bin_attrs[] = {
> +	&p2pmem_alloc_attr,
> +	NULL,
> +};
> +
>  static const struct attribute_group p2pmem_group = {
>  	.attrs = p2pmem_attrs,
> +	.bin_attrs = p2pmem_bin_attrs,
>  	.name = "p2pmem",
>  };
>  
> +static void p2pdma_page_free(struct page *page)
> +{
> +	struct pci_p2pdma_pagemap *pgmap = to_p2p_pgmap(page->pgmap);
> +	struct percpu_ref *ref;
> +
> +	gen_pool_free_owner(pgmap->provider->p2pdma->pool,
> +			    (uintptr_t)page_to_virt(page), PAGE_SIZE,
> +			    (void **)&ref);
> +	percpu_ref_put(ref);
> +}
> +
> +static const struct dev_pagemap_ops p2pdma_pgmap_ops = {
> +	.page_free = p2pdma_page_free,
> +};
> +
>  static void pci_p2pdma_release(void *data)
>  {
>  	struct pci_dev *pdev = data;
> @@ -152,6 +257,19 @@ static int pci_p2pdma_setup(struct pci_dev *pdev)
>  	return error;
>  }
>  
> +static void pci_p2pdma_unmap_mappings(void *data)
> +{
> +	struct pci_dev *pdev = data;
> +
> +	/*
> +	 * Removing the alloc attribute from sysfs will call
> +	 * unmap_mapping_range() on the inode, teardown any existing userspace
> +	 * mappings and prevent new ones from being created.
> +	 */
> +	sysfs_remove_file_from_group(&pdev->dev.kobj, &p2pmem_alloc_attr.attr,
> +				     p2pmem_group.name);
> +}
> +
>  /**
>   * pci_p2pdma_add_resource - add memory for use as p2p memory
>   * @pdev: the device to add the memory to
> @@ -198,6 +316,7 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
>  	pgmap->range.end = pgmap->range.start + size - 1;
>  	pgmap->nr_range = 1;
>  	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
> +	pgmap->ops = &p2pdma_pgmap_ops;
>  
>  	p2p_pgmap->provider = pdev;
>  	p2p_pgmap->bus_offset = pci_bus_address(pdev, bar) -
> @@ -209,6 +328,11 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
>  		goto pgmap_free;
>  	}
>  
> +	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_unmap_mappings,
> +					 pdev);
> +	if (error)
> +		goto pages_free;
> +
>  	p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
>  	error = gen_pool_add_owner(p2pdma->pool, (unsigned long)addr,
>  			pci_bus_address(pdev, bar) + offset,
> -- 
> 2.30.2
>