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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