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SubjectRe: [PATCH v4] xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE
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Hi,

On 10/04/18 08:58, Paul Durrant wrote:
> +static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
> +{
> + struct privcmd_data *data = file->private_data;
> + struct mm_struct *mm = current->mm;
> + struct vm_area_struct *vma;
> + struct privcmd_mmap_resource kdata;
> + xen_pfn_t *pfns = NULL;
> + struct xen_mem_acquire_resource xdata;
> + int rc;
> +
> + if (copy_from_user(&kdata, udata, sizeof(kdata)))
> + return -EFAULT;
> +
> + /* If restriction is in place, check the domid matches */
> + if (data->domid != DOMID_INVALID && data->domid != kdata.dom)
> + return -EPERM;
> +
> + down_write(&mm->mmap_sem);
> +
> + vma = find_vma(mm, kdata.addr);
> + if (!vma || vma->vm_ops != &privcmd_vm_ops) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + pfns = kcalloc(kdata.num, sizeof(*pfns), GFP_KERNEL);
> + if (!pfns) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> + if (xen_feature(XENFEAT_auto_translated_physmap)) {
> + struct page **pages;
> + unsigned int i;
> +
> + rc = alloc_empty_pages(vma, kdata.num);
> + if (rc < 0)
> + goto out;
> +
> + pages = vma->vm_private_data;
> + for (i = 0; i < kdata.num; i++)
> + pfns[i] = page_to_pfn(pages[i]);

I don't think this is going to work well if the hypervisor is using a
different granularity for the page.

Imagine Xen is using 4K but the kernel 64K. You would end up to have the
resource not mapped contiguously in the memory.

Cheers,

--
Julien Grall

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