On 05.06.25 17:37, Fuad Tabba wrote:
This patch enables support for shared memory in guest_memfd, including
mapping that memory from host userspace.
This functionality is gated by the KVM_GMEM_SHARED_MEM Kconfig option,
and enabled for a given instance by the GUEST_MEMFD_FLAG_SUPPORT_SHARED
flag at creation time.
Co-developed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
---
[...]
+static bool kvm_gmem_supports_shared(struct inode *inode)
+{
+ u64 flags;
+
+ if (!IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM))
+ return false;
+
+ flags = (u64)inode->i_private;
Can probably do above
const u64 flags = (u64)inode->i_private;
+
+ return flags & GUEST_MEMFD_FLAG_SUPPORT_SHARED;
+}
+
+static vm_fault_t kvm_gmem_fault_shared(struct vm_fault *vmf)
+{
+ struct inode *inode = file_inode(vmf->vma->vm_file);
+ struct folio *folio;
+ vm_fault_t ret = VM_FAULT_LOCKED;
+
+ if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
+ return VM_FAULT_SIGBUS;
+
+ folio = kvm_gmem_get_folio(inode, vmf->pgoff);
+ if (IS_ERR(folio)) {
+ int err = PTR_ERR(folio);
+
+ if (err == -EAGAIN)
+ return VM_FAULT_RETRY;
+
+ return vmf_error(err);
+ }
+
+ if (WARN_ON_ONCE(folio_test_large(folio))) {
+ ret = VM_FAULT_SIGBUS;
+ goto out_folio;
+ }
+
+ if (!folio_test_uptodate(folio)) {
+ clear_highpage(folio_page(folio, 0));
+ kvm_gmem_mark_prepared(folio);
+ }
+
+ vmf->page = folio_file_page(folio, vmf->pgoff);
+
+out_folio:
+ if (ret != VM_FAULT_LOCKED) {
+ folio_unlock(folio);
+ folio_put(folio);
+ }
+
+ return ret;
+}
+
+static const struct vm_operations_struct kvm_gmem_vm_ops = {
+ .fault = kvm_gmem_fault_shared,
+};
+
+static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ if (!kvm_gmem_supports_shared(file_inode(file)))
+ return -ENODEV;
+
+ if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) !=
+ (VM_SHARED | VM_MAYSHARE)) {
+ return -EINVAL;
+ }
+
+ vma->vm_ops = &kvm_gmem_vm_ops;
+
+ return 0;
+}
+
static struct file_operations kvm_gmem_fops = {
+ .mmap = kvm_gmem_mmap,
.open = generic_file_open,
.release = kvm_gmem_release,
.fallocate = kvm_gmem_fallocate,
@@ -428,6 +500,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
}
file->f_flags |= O_LARGEFILE;
+ allow_write_access(file);
Why is that required?
As the docs mention, it must be paired with a previous deny_write_access().
... and I don't find similar usage anywhere else.
Apart from that here
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
