Re: [PATCH v11 8/9] PCI/P2PDMA: Allow userspace VMA allocations through sysfs

Chaitanya Kulkarni
2022-10-25T01:34:31Z

On 10/21/22 10:41, 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>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> drivers/pci/p2pdma.c | 124 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 124 insertions(+)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 88dc66ee1c46..27539770a613 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,

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck